PubMed Health⌕ Search

Biomedical subjects

William J Evans

Publications and source records attributed to William J Evans.

At least 19 recordsLinked to original sources
PubMed2007

Efficacy and feasibility of a novel tri-modal robust exercise prescription in a retirement community: a randomized, controlled trial.

OBJECTIVES: To test the feasibility and efficacy of current guidelines for multimodal exercise programs in older adults. DESIGN: Randomized, controlled trial. SETTING: Retirement village. PARTICIPANTS: Thirty-eight subjects (14 men and 24 women) aged 76.6 +/- 6.1. INTERVENTION: A wait list control or 10 weeks of supervised exercise consisting of high-intensity (80% of one-repetition maximum (1RM)) progressive resistance training (PRT) 3 days per week, moderate-intensity (rating of perceived exertion 11 to 14/20) aerobic training 2 days per week, and progressive balance training 1 day per week. MEASUREMENTS: Blinded assessments of dynamic muscle strength (1RM), balance, 6-minute walk, gait velocity, chair stand, stair climb, depressive symptoms, self-efficacy, and habitual physical activity level. RESULTS: Higher baseline strength and psychological well-being were associated with better functional performance. Strength gains over 10 weeks averaged 39+/-31% in exercise, versus 21+/-24% in controls (P=.10), with greater improvements in hip flexion (P=.01), hip abduction (P=.02), and chest press (P=.04) in the exercise group. Strength adaptations were greatest in exercises in which the intended continuous progressive overload was achieved. Stair climb power (12.3+/-15%, P=.002) and chair stand time (-7.1+/-15%, P=.006) improved significantly and similarly in both groups. Reduction in depressive symptoms was significantly related to compliance (attendance rate r=-0.568, P=.009, PRT progression in loading r=-0.587, P=.02, and total volume of aerobic training r=-0.541, P=.01), as well as improvements in muscle strength (r=-0.498, P=.002). CONCLUSION: Robust physical and psychological adaptations to exercise are linked, although volumes and intensities of multiple exercise modalities sufficient to cause significant adaptation appear difficult to prescribe and adhere to simultaneously in older adults.

Aged↗
PubMed2006

Synthesis, structure, and 15N NMR studies of paramagnetic lanthanide complexes obtained by reduction of dinitrogen.

The recently discovered LnZ3/M and LnZ2Z'/M methods of reduction (Ln = lanthanide; M = alkali metal; Z, Z' = monoanionic ligands that allow these combinations to generate "LnZ2" reactivity) have been applied to provide the first crystallographically characterized dinitrogen complexes of cerium, [C5Me5)2(THF)Ce]2(mu-eta2.eta2-N2) and [(C5Me4H)2(THF)Ce]2(mu-eta2.eta2-N2), so that the utility of 15N NMR spectroscopy with paramagnetic lanthanides could be determined. [(C5Me5)2(THF)Pr]2(mu-eta2.eta2-N2) and [(C5Me4H)2(THF)Pr]2(mu-eta2.eta2-N2) were also synthesized, crystallographically characterized, and studied by 15N NMR methods. The data were compared to those of [(C5Me5)2Sm]2(mu-eta2.eta2-N2). [(C5Me5)2(THF)Ce]2(mu-eta2.eta2-N2) and [(C5Me5)2(THF)Pr]2(mu-eta2.eta2-N2) are unlike their (C5Me4H)1- analogs in that the solvating THF molecules are cis rather than trans. Structural information on precursors, (C5Me4H)3Ce, (C5Me4H)3Pr, and the oxidation product [(C5Me5)2Ce]2(mu-O) is also presented.

Journal Article↗
PubMed2006

Planar trimethylenemethane dianion chemistry of lanthanide metallocenes: synthesis, structure, density functional theory analysis, and reactivity of [(C5Me5)2Ln]2[mu-eta3:eta3-C(CH2)(3] Complexes.

The unusual formation of planar trimethylenemethane (TMM) dianion complexes of lanthanide metallocenes, [(C5Me5)2Ln]2[mu-eta3:eta3-C(CH2)3] (Ln = Sm, 1; La, 2; Pr, 3; Nd, 4; Y, 5) has been examined by synthesizing examples with metals from La to Y to examine the effects of radial size on structure and to provide closed shell examples for direct comparison with density functional theory (DFT) calculations. Synthetic routes to 1-4 have been expanded from the [(C5Me5)2Ln][(mu-Ph)2BPh2]/neopentyl lithium reaction involving beta-methyl elimination to a [(C5Me5)2Ln][(mu-Ph)2BPh2]/isobutyl lithium route. The synthetic pathways are sensitive to metal radius. To obtain 5, the methylallyl complex, (C5Me5)2Y[CH2C(Me)CH2], 6, was synthesized and treated with [(C5Me5)2YH]x. In the Lu case, the neopentyl complex [(C5Me5)2LuCH2C(CH3)3]x, 7, was isolated instead of the TMM product. X-ray crystallography showed that the metrical parameters of the planar TMM dianions in each complex are similar. The structural data have been compared with DFT calculations on the closed-shell lanthanum and lutetium complexes that suggest only limited covalent interactions with the lanthanide ion. Benzophenone (2 equiv) reacts with 1 to expand the original four-carbon TMM skeleton to a dianionic bis(alkoxide) ligand containing a symmetrically substituted C=CH2 moiety in [(C5Me5)2Sm]2[mu-(OCPh2CH2)2C=CH2], 8. In this reaction, the TMM complex reacts as a bifunctional bisallylic reagent that generates an organic framework containing a central vinyl group.

Journal Article↗
PubMed2006

Organolutetium vinyl and tuck-over complexes via C-H bond activation.

The vinyl C-H bond of tetramethylfulvene is activated in the presence of [(C5Me5)2LuH]x, 1, to form a vinyl organolutetium complex, (C5Me5)2Lu(CH=C5Me4), 2. Also formed in the reaction is the "tuck-over" complex, (C5Me5)2Lu(mu-H)(mu-eta1:eta5-CH2C5Me4)Lu(C5Me5), 3, containing a (CH2C5Me4)2- moiety long postulated to exist in organolutetium chemistry but never crystallographically characterized. Evidence for these C-H bond activations by a "(C5Me5)3Lu" intermediate, 4, is presented. Complex 3 can also be made in high yield by thermolysis of 1. Under H2, 1 catalytically hydrogenates TMF to C5Me5H.

Journal Article↗
PubMed2006

Trivalent [(C5Me5)2(THF)Ln]2(mu-eta2:eta2-N2) complexes as reducing agents including the reductive homologation of CO to a ketene carboxylate, (mu-eta4-O2C-C=C=O)2-.

The [Z(2)Ln(THF)](2)(mu-eta(2)():eta(2)()-N(2)) complexes (Z = monoanionic ligand) generated by reduction of dinitrogen with trivalent lanthanide salts and alkali metals are strong reductants in their own right and provide another option in reductive lanthanide chemistry. Hence, lanthanide-based reduction chemistry can be effected in a diamagnetic trivalent system using the dinitrogen reduction product, [(C(5)Me(5))(2)(THF)La](2)(mu-eta(2)():eta(2)()-N(2)), 1, readily obtained from [(C(5)Me(5))(2)La][BPh(4)], KC(8), and N(2). Complex 1 reduces phenazine, cyclooctatetraene, anthracene, and azobenzene to form [(C(5)Me(5))(2)La](2)[mu-eta(3):eta(3)-(C(12)H(8)N(2))], 2, (C(5)Me(5))La(C(8)H(8)), 3, [(C(5)Me(5))(2)La](2)[mu-eta(3):eta(3)-(C(14)H(10))], 4, and [(C(5)Me(5))La(mu-eta(2)-(PhNNPh)(THF)](2), 5, respectively. Neither stilbene nor naphthalene are reduced by 1, but 1 reduces CO to make the ketene carboxylate complex {[(C(5)Me(5))(2)La](2)[mu-eta(4)-O(2)C-C=C=O](THF)}(2), 6, that contains CO-derived carbon atoms completely free of oxygen.

Journal Article↗
PubMed2006

Solid-state 139La and 15N NMR spectroscopy of lanthanum-containing metallocenes.

A preliminary set of solid-state 139La and 15N NMR data for lanthanum-containing metallocenes is presented, including (C5H5)3La, (C5Me4H)3La, [(C5Me5)2La]+[BPh4]-, and 15N-enriched [(C5Me4H)2La(THF)]215N2. Broad 139La NMR spectra, with breadths ranging from 600 kHz to 2.5 MHz, were acquired with piecewise QCPMG techniques at 9.4 T. Simulations of the spectra reveal 139La quadrupolar coupling constants (CQ) between 44 and 105 MHz. In addition, the first NMR measurement of a nitrogen chemical shift (CS) tensor for dinitrogen bound side-on to a metal atom is reported for [(C5Me4H)2La(THF)]215N2. The 139La NMR parameters show remarkable sensitivity to changes in metallocene structure and can be interpreted in an intuitive manner. Preliminary RHF and DFT calculations of 139La electric field gradient (EFG) and nitrogen CS tensors are used to provide tensor orientations and to rationalize the origin of the NMR parameters in terms of molecular structure and symmetry. The sensitivity of 139La and 15N NMR tensor parameters to changes in structure and bonding should prove invaluable in future studies of noncrystalline and disordered systems.

Journal Article↗
PubMed2006

C-H bond activation through steric crowding of normally inert ligands in the sterically crowded gadolinium and yttrium (C5Me5)3M complexes.

Synthesis of the sterically crowded Tris(pentamethylcyclopentadienyl) lanthanide complexes, (C5Me5)3Ln, has demonstrated that organometallic complexes with unconventionally long metal ligand bond lengths can be isolated that provide options to develop new types of ligand reactivity based on steric crowding. Previously, the (C5Me5)3M complexes were known only with the larger lanthanides, La-Sm. The synthesis of even more crowded complexes of the smaller metals Gd and Y is reported here. These complexes allow an evaluation of the size/reactivity correlations previously limited to the larger metals and demonstrate a previously undescribed type of C5Me5-based reaction, namely C-H bond activation. (C5Me5)3Gd, was prepared from GdCl3 through (C5Me5)2GdCl2K(THF)2, (C5Me5)2Gd(C3H5), and [(C5Me5)2Gd][BPh4] and structurally characterized by x-ray crystallography. Although Gd3+ is redox-inactive, (C5Me5)3Gd functions as a reducing agent in reactions with 1,3,5,7-cyclooctatetraene (COT) and triphenylphosphine selenide to make (C5Me5)Gd(C8H8), [(C5Me5)2Gd]2Se2, and [(C5Me5)2Gd]2Se depending on the stoichiometry used. When the analogous synthetic method was attempted with yttrium in arene solvents, the previously characterized (C5Me5)2YR complexes (R=C6H5, CH2C6H5) were isolated instead, i.e., C-H bond activation of solvent occurred. To avoid this problem, (C5Me5)3Y was synthesized in high yield from [(C5Me5)2YH]2 and tetramethylfulvene in aliphatic solvents. Isolated (C5Me5)3Y was found to metalate benzene and toluene with concomitant formation of C5Me5H, a reaction contrary to the normal pKa values of these hydrocarbons. In this case, the normally inert (C5Me5)1- ligand engages in C-H bond activation due to the extreme steric crowding.

Journal Article↗
PubMed2006

Lanthanum and alkali metal coordination chemistry of the bis(dimethylphenylsilyl)amide ligand.

The coordination chemistry of the bis(dimethylphenylsilyl)amide ligand, [N(SiMe2Ph)2]1-, with sodium, potassium, and lanthanum has been investigated for comparison with the more commonly used [N(SiMe3)2]1- and [N(SiHMe2)2]1- ligands. HN(SiMe2Ph)2 reacts with KH to produce KN(SiMe2Ph)2, 1, which crystallizes from toluene as the dimer [KN(SiMe2Ph)2(C7H8)]2, 2. The structure of 2 shows that the [N(SiMe2Ph)2]1- ligand can function as a polyhapto ligand with coordination from each phenyl group as well as the normal nitrogen ligation and agostic methyl interactions common in methylsilylamides. Each potassium in 2 is ligated by an eta4-toluene, two bridging nitrogen atoms, and an eta2-phenyl, an eta1-phenyl, and an eta1-methyl group. KN(SiMe2Ph)2 crystallizes from toluene in the presence of 18-crown-6 to make the monometallic complex (18-crown-6)KN(SiMe2Ph)2, 3, in which [N(SiMe2Ph)2]1- functions as a simple monodentate ligand through nitrogen. The reaction of HN(SiMe2Ph)2 with NaH in THF at reflux for 2 days generates Na[N(SiMe2Ph)2], 4, which crystallizes as the solvated dimer {(THF)Na[mu-eta1:eta1-N(SiMe2Ph)2]}2, 5. A lanthanide metallocene derivative of [N(SiMe2Ph)2]1- was obtained by reaction of K[N(SiMe2Ph)2] with [(C5Me5)2La][(mu-Ph)2BPh2]. Crystals of (C5Me5)2La[N(SiMe2Ph)2], 6, show agostic interactions between lanthanum and methyl groups of each silyl substituent. The [N(SiMe3)2]1- analogue of 3, (18-crown-6)KN(SiMe3)2, 7, was also structurally characterized for comparison.

Journal Article↗
PubMed2006

Aging alters macrophage properties in human skeletal muscle both at rest and in response to acute resistance exercise.

Macrophages are involved in skeletal muscle repair through pro-inflammatory and alternative functions. We tested the hypothesis that aging alters the abundance and properties of skeletal muscle macrophages that will influence their functional response to acute resistance exercise. Total macrophages (CD 68+), as well as pro- (CD 11b+) and anti-inflammatory (CD 163+) subpopulations and associated cytokine mRNAs were quantified in vastus lateralis biopsies from young (N=17) and elderly (N=17) males pre- and 72 h post-exercise. Pre-exercise, young muscle tended to possess a greater number of macrophages, whereas elderly muscle possessed higher levels of IL-1 beta (P=0.001), IL-1 RA (P=0.003), and IL-10 (P=0.028). Post-exercise, total macrophages did not change in either group, however, the number of CD 11b+ (P=0.039) and CD 163+ (P=0.026) cells increased 55 and 29%, respectively, but only in the young. IL-1 beta (P=0.006), IL-10 (P=0.016), and AMAC-1 (P=0.044) also increased, approximately two-fold, and again only in the young. Quantitation of CD 11b+ and CD 163+ cells suggests that the majority of resident macrophages possess alternative functions, and a small subpopulation participates in the inflammatory response. Both subpopulations increased their activity post-exercise, exclusively in the young. These findings suggest that aging results in a defective regulation of muscle macrophage function, both at baseline and in response to resistance exercise, that may limit muscle hypertrophy in older adults.

Adult↗
PubMed2006

Synthesis of (O2CEPh)1- ligands (E = S, Se) by CO2 insertion into lanthanide chalcogen bonds and their utility in forming crystallographically characterizable organoaluminum complexes [Me2Al(mu-O2CEPh)]2.

CO(2) inserts into the Sm-S and Sm-Se bonds of [(C(5)Me(5))(2)Sm(mu-EPh)](2) (E = S, Se) to form the first crystallographically characterized (O(2)CEPh)(1-) complexes, [(C(5)Me(5))(2)Sm(mu-O(2)CEPh)](2). These complexes are structurally analogous to [(C(5)Me(5))(2)Sm(mu-O(2)CR)](2) complexes, but they are less soluble. This feature was utilized in the reaction of Me(2)AlCl with [(C(5)Me(5))(2)Sm(mu-O(2)CEPh)](2), which forms crystallographically characterizable [Me(2)Al(mu-O(2)CEPh)](2) complexes. Such complexes could not be isolated from an analogous carboxylate reaction. [(C(5)Me(5))(2)Sm(mu-O(2)CSePh)](2) decarboxylates in THF to form (C(5)Me(5))(2)Sm(SePh)(THF). The loss of CO(2) rather than COSe with formation of (C(5)Me(5))(2)Sm(OPh)(THF) was established by (13)CO(2) studies and independent synthesis of (C(5)Me(5))(2)Sm(OPh)(THF) from (C(5)Me(5))(2)Sm[N(SiMe(3))(2)] and PhOH.

Journal Article↗
PubMed2006

Predictors of weight loss in Parkinson's disease.

The objective of this study was to examine the change of body weight (BW) among Parkinson's disease (PD) patients and controls over years and determine the predictors of weight loss among PD patients. Studies on weight loss in PD studies are cross-sectional, have a short follow-up, or lack in clinical detail. We examined the percentage of BW change over years among 49 PD patients and 78 controls. The controls were from another study on longitudinal evolution of BW and body composition in the elderly. We determined the BW, Hoehn and Yahr (HY) stage, and dyskinesia status of 49 consecutive nondemented PD patients with symptom duration of 6.1 +/- 0.7 years (mean +/- SEM) and ascertained their BW at the time of diagnosis and 2.4 +/- 0.2 years before the diagnosis from medical records. We collected data again 7.2 +/- 0.5 years after the first visit. The PD group lost 7.7% +/- 1.5% of BW over the entire symptomatic period (13.1 +/- 0.8 years), while the control group lost only 0.2% +/- 0.7% of BW over 9.9 +/- 0.1 years; weight loss was clinically significant (>5%) in 55.6% of PD patients vs. 20.5% of the controls (both P values < 0.001, adjusted for sex, baseline age, and observation period duration). PD patients lost weight in both the early and advanced phases. While worsening of parkinsonism was the most important factor, age at diagnosis, emergence of visual hallucinations, and possibly dementia were also associated with weight loss. We demonstrated significant weight loss in PD patients compared to controls over approximately 1 decade. Neurodegeneration involving both motor and nonmotor systems may be associated with weight loss in PD.

Aged↗
PubMed2006

Comparison of insulin sensitivity assessment indices with euglycemic-hyperinsulinemic clamp data after a dietary and exercise intervention in older adults.

Multiple indices to assess insulin sensitivity calculated from mathematical equations based on fasting blood parameters or oral glucose tolerance data have been developed. Although these indices have frequently been validated using euglycemic-hyperinsulinemic clamp data, the utility of each equation in measuring change in insulin sensitivity over time remains uncertain. We examined change in insulin sensitivity in response to a 12-week diet and exercise intervention in 31 older men and women with impaired glucose tolerance using a euglycemic-hyperinsulinemic clamp and 10 commonly used insulin sensitivity equations. Mean glucose disposal as calculated from clamp data was significantly higher after the intervention compared with baseline (5.92 +/- 0.38 vs 5.18 +/- 0.30 mg . kg fat free mass(-1) . min(-1), P = .013). In contrast, none of the examined indices indicated a significant change in insulin sensitivity over time (all P > .3). A limits of agreement approach to compare insulin sensitivity calculated from each equation with the measure of glucose disposal from the clamp indicated overall imperfect agreement between measures (agreement limits ranged from +/-2.48 to +/-4.23 mg . kg fat free mass(-1) . min(-1)) despite significant bivariate correlations between indices and clamp data. The wide variability in the 95% prediction limits of agreement among equations suggests that these equations vary substantially from a euglycemic-hyperinsulinemic clamp in their ability to assess insulin sensitivity. Despite the observed limited agreement using this statistical approach, changes in several calculated indices were significantly correlated with changes in clamp data, suggesting that these indices may have some utility in tracking improvements in insulin sensitivity. Further research is necessary to examine agreement between indices and clamp data in larger, more heterogeneous populations and in response to other interventions where the magnitude of change in insulin sensitivity may be larger.

Aged↗
PubMed2006

Effects of an ad libitum, high carbohydrate diet and aerobic exercise training on insulin action and muscle metabolism in older men and women.

BACKGROUND: Previous studies have demonstrated that aerobic exercise training and weight loss have independent effects on insulin-stimulated glucose disposal (ISGD). We hypothesized that ad libitum consumption of a high-carbohydrate diet would result in weight loss and improved ISGD, and that aerobic exercise training would facilitate greater improvements in ISGD compared with diet alone. METHODS: Older participants (13 women, 9 men; age = 66 +/- 1 year) with impaired glucose tolerance were randomly assigned to an ad libitum diet alone (18% fat, 19% protein, 63% carbohydrate) or this diet plus aerobic exercise training (4 d/wk, 45 min/d, 80% VO(2peak)) for 12 weeks. ISGD, abdominal fat distribution, muscle glycogen, and glycogen synthase activity were assessed pre- and postintervention. RESULTS: Consumption of the diet resulted in significant weight loss and an improvement in ISGD. Consumption of the diet plus exercise training also resulted in weight loss and increased ISGD, but results were not significantly different from those in the diet-alone group. Mean abdominal visceral and subcutaneous adipose tissue cross-sectional areas were smaller postintervention compared to baseline with no difference between groups. Exercise training and consumption of the diet increased muscle glycogen content (344.7 +/- 21.3 to 616.7 +/- 34.4 micromol.g(-1)) and decreased glycogen synthase activity (0.21 +/- 0.02 to 0.13 +/- 0.01) compared to the diet alone. CONCLUSIONS: These results demonstrate that consumption of an ad libitum, high-carbohydrate diet alone or in combination with aerobic exercise training results in weight loss and improved insulin sensitivity. Furthermore, exercise combined with this diet appears to limit additional increases in insulin sensitivity due to muscle glycogen supercompensation with a concomitant adaptive response of glycogen synthase.

Aged↗
PubMed2006

Exercise-induced changes in insulin action and glycogen metabolism in elderly adults.

PURPOSE: Although data suggest that physical activity is associated with decreased insulin resistance, recommendations for exercise training are not specific for age or level of obesity. Therefore, we examined the influence of moderate-intensity (50% of VO2max) exercise training (MI) versus high-intensity (75% of VO2max) exercise training (HI) on insulin-stimulated glucose disposal (ISGD) in elderly individuals. METHODS: Following medical examinations, 21 overweight (body mass index = 29 +/- 1 kg x m(-2)) elderly (74 +/- 1 yr) subjects were randomized to 1) HI, 2) MI, or a 3) nonexercising control group. Subjects enrolled in HI or MI completed a 12-wk exercise training regimen designed to expend 1000 kcal x wk. ISGD was assessed using a hyperinsulinemic, euglycemic clamp pre- and postintervention. ISGD was corrected for hepatic glucose production (glucose Ra) using a constant rate infusion of [6,6-H2]glucose and determined during the last 30 min of the clamp by subtracting glucose Ra from the exogenous glucose infusion rate. Nonoxidative glucose disposal was calculated using indirect calorimetry. Body composition testing was completed using dual energy x-ray absorptiometry. RESULTS: ISGD increased by approximately 20% with HI (Delta of 1.4 +/- 0.5 mg x kg(-1) FFM.min(-1)). However, ISGD did not change (Delta of -0.4 +/- 0.1 mg x kg(-1) FFM.min(-1)) with MI and was not different (Delta of -0.2 +/- 0.1 mg x kg(-1) FFM.min(-1)) in the control group. Nonoxidative glucose disposal increased with HI (Delta of 1.4 +/- 0.5 mg x kg(-1) FFM.min(-1)), but there was no change in nonoxidative glucose disposal with MI or in the control group. No change in body weight or percentage of body fat was observed in any group. CONCLUSION: In weight-stable subjects, MI resulted in no change in ISGD, and the improvement in ISGD with HI was completely reliant on improvements in nonoxidative glucose disposal.

Aged↗
PubMed2005

Methyl displacements from cyclopentadienyl ring planes in sterically crowded (C5Me5)3M complexes.

The displacements of the methyl substituents away from the metal and out of the cyclopentadienyl ring plane are compared in sterically crowded (C(5)Me(5))(3)M complexes vs sterically normal f-element complexes in an attempt to evaluate the utility of this parameter in predicting unusual (C(5)Me(5))(1-) ring reactivity. The out-of-plane displacements of 16 sterically crowded tris(cyclopentadienyl) complexes of general formula (C(5)Me(5))(3)M, (C(5)Me(4)R)(3)M (R = Et, (i)Pr, (t)()Bu, SiMe(3)), (C(5)Me(5))(3)MX (X = anion), and (C(5)Me(5))(3)ML (L = neutral ligand) are compared with [(C(5)Me(5))(2)U](2)(C(6)H(6)), (C(5)Me(5))(2)Sm(PC(4)H(2)(t)Bu(2)), and 33 representative examples of f-element bis(cyclopentadienyl) complexes with normal cyclopentadienyl behavior and coordination numbers ranging from 6 to 10. In general, the methyl displacement values of sterically crowded complexes overlap with those in the other complexes, which demonstrates that the basis of the structural distortions is complex. However, if the most extreme out-of-plane displacement in each of the sterically crowded complexes is examined vs the analogous maximum out-of-plane displacement in less crowded systems, there appears to be a basis for predicting cyclopentadienyl reactivity.

Journal Article↗
PubMed2005

Molecular octa-uranium rings with alternating nitride and azide bridges.

Uranium nitrides offer potential as future nuclear fuels and as probes of metal ligand multiple bonding involving the f-block actinide metals. However, few molecular examples are available for study owing to the difficulties in synthesis. Recent advances in organoactinide chemistry have provided a route to uranium nitride complexes that expands the options for developing UN chemistry. Several 24-membered uranium nitrogen rings, (UNUN3)4, have been synthesized by reduction of sodium azide with organometallic metallocene derivatives, [(C5Me4R)2U][(mu-Ph)2BPh2] (R = Me, H; Me = methyl, Ph = phenyl). The nanometer-sized rings contain unusual UNU nitride linkages that have short U-N distances within the double-bond range.

Journal Article↗
PubMed2005

[(C5Me5)2U][(mu-Ph)2BPh2] as a four electron reductant.

Examination of the reactivity of [(C5Me5)2U][(mu-Ph)2BPh2] as a "blank" for comparison with the four- and eight-electron reductive chemistry of the sterically crowded (C5Me5)3U and [(C5Me5)2U]2(C6H6) complexes revealed that the tetraphenylborate complex surprisingly functions as a four-electron reductant by combining [BPh4]1- and U(III) reduction; all three complexes cleave the N=N bond in PhN=NPh to form the bis(organoimido) U(VI) complex, (C5Me5)2U(NPh)2, and they also reduce PhC[triple bond]CPh to form (C5Me5)2U(C4Ph4).

Journal Article↗