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Andrew D Phillips

Publications and source records attributed to Andrew D Phillips.

At least 19 recordsLinked to original sources
PubMed2006

A counterintuitive structural effect of metal-metal bond protonation and its electronic underpinnings.

Protonation across the metal-metal bond in the complexes [(CO)(2)M(mu-dppm)(mu-PtBu(2))(mu-H)M(CO)(2)] (M=Fe or Ru, dppm=Ph(2)PCH(2)PPh(2)) induces M-M bond shortening of up to about 0.05 A. DFT calculations on simplified iron models reproduce this trend well. Conversely, the computations show that the M-M distance in the dimer [{Cp*Ir(CO)}(2)] lengthens with two consecutive protonations, but there are no crystal structure determinations to highlight the effects on the Ir-Ir bond. DFT calculations and the analogous cobalt system confirm that the transformation of a two-electron, two-center (2e-2c) bond into a 2e-3c bond is accompanied by the predicted elongation. An MO analysis indicated similar nature and evolution of the M-M bonding these cases. In particular, the HOMOs of the mono-hydrido cations [Cp(CO)M(mu-H)M(CO)Cp](+) (M=Ir, Co) have evident M-M bent-bond character, and hence subsequent protonation invariably causes a decrease in the bond index. The Fe(2) and Co(2) systems have also been analyzed with the quantum theory of atoms in molecules (QTAIM) method, but in no case was an M-M bond critical point located unless an artificially shorter M-M distance was imposed. However, the trends for the atoms-in-molecules (AIM) bond delocalization indexes delta(M-M) confirm the overall M-M bond weakening on protonation. In conclusion, all the computational results for the iron system indicate that the paradigm of a direct correlation between bond strength and distance is not always applicable. This is attributable to a very flat potential energy surface and various competing effects imposed by the bridging ligands.

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PubMed2006

Experimental and computational studies on the solvent-controlled cluster isomerism of Ru3(H)(CO)9(NPPh3) and related dynamics.

The species Ru3(H)(mu3-NPPh3)(CO)9 occurs in the solid state as two isomers, characterized either by one capping hydride and three CO bridges (1a) or by one bridging hydride and all terminals COs (1b); key intermediates for the formation, fluxionality and solvent-dependent interconversion of the isomers are highlighted through a DFT MO analysis.

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PubMed2005

Synthesis and reactivity of dimeric Ar'TlTlAr' and trimeric (Ar"T1)3 (Ar', Ar" = bulky terphenyl group) thallium(I) derivatives: Tl(I)-Tl(I) bonding in species ligated by monodentate ligands.

The synthesis and characterization of three new organothallium(I) compounds are reported. Reaction of (Ar'Li)(2) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) and Ar"Li (Ar" = C(6)H(3)-2,6-(C(6)H(3)-2,6-Me(2))(2)) with TlCl in Et(2)O afforded (Ar'Tl)(2) (1) and (Ar' 'Tl)(3) (2). The "dithallene" 1 is the heaviest group 13 dimetallene and features a planar, trans-bent structure with Ar'Tl-Tl = 119.74(14) degrees and Tl-Tl = 3.0936(8) A. Compound 2 is the first structurally characterized neutral, three-membered ring species of formula c-(MR)(3) (M = Al-Tl; R = organo group). The Tl(3) ring has Tl-Tl distances in the range ca. 3.21-3.37 A as well as pyramidal Tl geometries. The Tl-Tl bonds in 1 and 2 are outside the range (2.88-2.97 A) of Tl-Tl single bonds in R(2)TlTlR(2) compounds. The weak Tl-Tl bonding in 1 and 2 leads to their dissociation into Ar'Tl and Ar' 'Tl monomers in hexane. The Ar'Tl monomer behaves as a Lewis base and readily forms a 1:1 donor-acceptor complex with B(C(6)F(5))(3) to give Ar'TlB(C(6)F(5))(3), 3. Adduct 3 features an almost linear thallium C(ipso)-Tl-B angle of 174.358(7) degrees and a Tl-B distance of 2.311(2) A, which indicates strong association. Treatment of 1 with a variety of reagents resulted in no reactions. The lower reactivity of 1 is in accord with the reluctance of Tl(I) to undergo oxidation to Tl(III) due to the unreactive character of the 6s(2) electrons.

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PubMed2005

Hypervalent, low-coordinate phosphorus(III) centers in complexes of the phosphadiazonium cation with chelate ligands.

Trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphine, Mes*NPOTf (Mes = 2,4,6-tri-tert-butylphenyl, OTf = trifluoromethanesulfonate, triflate) reacts quantitatively with the multifunctional ligands 2,2'-bipyridine (2,2'-BIPY), N,N,N',N'-tetramethylethylenediamine (TMEDA), 1,2-bis(diethylphosphino)ethane (DEPE), 1,2-bis(diphenylphosphino)ethane (DIPHOS), and N,N,N',N' ',N' '-pentamethyldiethylenetriamine (PMDETA) to give the Lewis acid-base complexes [Mes*NP(2,2'-BIPY)][OTf], [Mes*NP(TMEDA)][OTf], [Mes*NP(DIPHOS)][OTf], [Mes*NP(DEPE)][OTf], and [Mes*NP(PMDETA)][OTf], respectively. Single-crystal X-ray diffraction studies indicate that the closest contact of the ligand donor atoms occurs at phosphorus in all cases, affecting significant displacement of the OTf anion. The resulting cations [Mes*NP(L)]+ are best described as complexes of a neutral chelating ligand on a phosphadiazonium Lewis acceptor, and highlight the potential for electron-rich centers to behave as Lewis acids despite the presence of a lone pair of electrons at the acceptor site. More importantly, the new complexes represent rare examples of systems containing hypervalent, low-coordinate phosphorus(III) centers.

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PubMed2004

Terphenyl ligand stabilized lead(II) derivatives: steric effects and lead-lead bonding in diplumbenes.

The reaction of PbBr(2) with the lithium reagents LiC(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2) (LiArPr(i)(2)) and Et(2)O.LiC(6)H(3)-2,6-(2,6-Pr(i)-4-Bu(t)C(6)H(2))(2) (Et(2)O.LiArPr(i)(2)Bu(t)) furnished the bromide bridged organolead(II) halides [Pb(mu-Br)ArPr(i)(2)](2) (1) and[Pb(mu-Br)ArPr(i)(2)Bu(t)](2) (2) as orange crystals. Treatment of 1 with a stoichiometric amount of methylmagnesium bromide resulted in the "diplumbene" Pr(i)(2)Ar(Me)PbPb(Me)ArPr(i)(2) (3). The addition of 1 equiv of 4-tert-butylphenylmagnesium bromide to 1 afforded the feebly associated, Pb-Pb bonded species [Pb(C(6)H(4)-4-Bu(t))ArPr(i)(2)](2) (4), whereas the corresponding reaction of tert-butylmagnesium chloride and 1 afforded the monomer Pb(Bu(t))ArPr(i)(2) (5). The reaction of the more crowded aryl lead(II) bromide [Pb(mu-Br)ArPr(i)(3)](2) (Ar = C(6)H(3)-2,6(C(6)H(2)-2,4,6-Pr(i)(3))(2)) with 4-isopropyl-benzylmagnesium bromide or LiSi(SiMe(3))(3) yielded the monomers 6, [Pb(CH(2)C(6)H(4)-4-Pr(i))ArPr(i)(3)], or 7, [Pb(Si(SiMe(3))(3))ArPr(i)(3)]. All compounds were characterized with use of X-ray crystallography, (1)H, (13)C, and (207)Pb NMR (3-7), and UV-vis spectroscopy. The dimeric Pb-Pb bonded (Pb-Pb = 3.1601(6) A) structure of 3 may be contrasted with the previously reported monomeric structure of Pb(Me)ArPr(i)(3), which differs from 3 only in that it has para Pr(i) substituents on the flanking aryl rings. The presence of these groups is sufficient to prevent the weak Pb-Pb bonding seen in 3. The dimer 4 displays a Pb-Pb distance of 3.947(1) A, which indicates a very weak lead-lead interaction, and it is possible that this close approach could be caused by packing effects. The monomeric structures of 6 and 7 are attributable to steric effects and, in particular, to the large size of ArPr(i)(3).

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PubMed2004

Ylidene-->iminophosphine coordination complexes and reversible dissociation of dichlorophosphetidines.

Chloro-, bromo-, iodo-, and trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphines (MesNPX; X = Cl, Br, I, OTf) react quantitatively with 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Im) to give Lewis acid-base complexes with the general formula MesNP(Im)X. The dichlorophosphetidine (DippNPCl)(2) (Dipp = 2,6-diisopropylphenyl) represents a formal cyclodimer of an iminophosphine and reacts with Im to give a similar complex. The process represents a ligand induced dissociation of the phosphetidine framework and is reversed by the introduction of an appropriate Lewis acid. Solid state structures of RNP(Im)X complexes show that the closest contact between acid and base occurs between phosphorus and carbon in all cases, highlighting them as compounds that contain examples of C-->P coordinate bonds. Association of Im with phosphorus also effects a substantial increase in the P-X distance, but all derivatives maintain a short NP bond, indicating the presence of NP pi-bonding.

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PubMed2003

Germanium and tin analogues of alkynes and their reduction products.

The reduction of terphenylgermanium(II) or terphenyltin(II) chlorides with alkali metals was investigated. Treatment of Ar'GeCl or ArGeCl (Ar' = C(6)H(3)-2,6-Dipp(2), Dipp = C(6)H(3)-2,6-Pr(i)(2); Ar = C(6)H(3)-2,6-Trip(2), Trip = C(6)H(2)-2,4,6-Pr(i)(3)) with lithium, sodium, or potassium afforded the neutral alkyne analogues Ar'GeGeAr', 1, ArGeGeAr, 2, the singly reduced radical species NaArGeGeAr, 3, or KAr'GeGeAr', 4, or the doubly reduced compounds Li(2)Ar'GeGeAr', 5, Na(2)ArGeGeAr, 6, or K(2)ArGeGeAr, 7. Similarly, reduction of Ar'SnCl or ArSnCl afforded the neutral Ar'SnSnAr', 8, or ArSnSnAr, 9, the radical anions [(THF)(3)Na[rSnSnAr]], 10, [K(THF)(6)][Ar'SnSnAr'], 11, [K(THF)(6)][ArSnSnAr], 12, [K(18-crown-6)(THF)(2)] [ArSnSnAr], 13, or the doubly reduced Na(2)ArSnSnAr, 14, K(2)Ar'SnSnAr', 15, or K(2)ArSnSnAr, 16. The compounds were characterized by UV-vis, (1)H and (13)C NMR or EPR spectroscopy. The X-ray crystal structures of all compounds were determined except those of 2 and 9. The neutral 1 and 8 displayed planar, trans-bent CMMC (M = Ge and Sn) cores with M-M-C angles of 128.67(8) and 125.24(7) degrees, respectively. The M-M bond lengths, 2.2850(6) and 2.6675(4)A, indicated considerable multiple character and a bond order approaching two. Single and double reduction of the neutral species resulted in the narrowing of the M-M-C angles by ca. 12-32 degrees and changes in the Ge-Ge and Sn-Sn bond lengths. One-electron reduction afforded a slight (ca. 0.03-0.05A) lengthening of the Ge-Ge bonds in the case of germanium species 3 and 4 and a greater lengthening (ca. 0.13-0.15A) for the Sn-Sn bonds in the tin compounds 10-13. The addition of another electron yielded salts of the formal dianions [Ar'MMAr'](2)(-) and [ArMMAr](2)(-) which are isoelectronic to the corresponding doubly bonded, neutral arsenic and antimony derivatives. All the dianion salts were obtained as contact ion triples with two alkali metal cations complexed between aryl rings. The Ge-Ge bonds in the dianions of 5-7 were longer, whereas the Sn-Sn distances in the dianions in 14, 15, and 16 were shorter than those in the monoanions. Unusually, the Li(2)Ar'GeGeAr' salt, 5, displayed a longer Ge-Ge bond (by ca. 0.06A) than those of its Na(+) or K(+) analogue salts which was attributed to the greater polarizing power of Li(+). It was concluded that the M-M bond lengths in 3-7 and 10-16 are dependent on several factors that include M-M-C angle, Coulombic repulsion, alkali metal cation size, and the character of the molecular energy levels. The M-M bonding in the neutral compounds was accounted for in terms of a second-order Jahn-Teller mixing of sigma- and a pi-orbital which afforded bond orders near two for the neutral compounds, 1, 2, 8, and 9. Calculations on MeMMMe (M = Ge or Sn) model species showed that the LUMO corresponded to an orbital that had n(+) lone pair character. The slight Ge-Ge bond length increase upon one-electron reduction is consistent with these results, and the further bond lengthening upon double reduction is consistent with increased Coulombic repulsion. The greater Sn-Sn bond length increase seen for one-electron reduction of the tin species is probably due to the increased p-character of orbitals comprising the Sn-Sn sigma-bond when the Sn-Sn-C angle is decreased by ca. 30 degrees. Upon further reduction, the slight decrease in the Sn-Sn bond is probably a result of the reduced importance of Coulombic repulsion due to the larger size of tin and a widening of the Sn-Sn-C angles which may shorten the Sn-Sn sigma-bond.

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PubMed2003

Chalcogeno-urea ligands on a phosphadiazonium Lewis acceptor: a new synthetic approach to Ch-P bonds (Ch = O, S, Se).

The isolation and characterization of the first intermolecular chalcogeno-urea complexes of iminophosphines are described. Trifluoromethylsulfonyloxy(2,4,6-tri-tert-butylphenylimino)phosphine, MesNPOTf, reacts quantitatively with chalcogenoimidazolines (ChIm, Ch = O, S, Se) and 1,3-dimethyldiphenylurea (OU) to give Lewis acid-base complexes, [MesNP.ChIm]OTf and [MesNP.OU]OTf. Single crystal X-ray diffraction studies indicate that the closest contact of the chalcogeno-urea donor occurs at phosphorus in all cases, representing compounds that contain examples of O-P, S-P, and Se-P coordinate bonds. In all complexes, coordination of the ligand causes significant displacement of the OTf anion, and the resulting cations [MesNP.L](+) are best described as complexes of a neutral ligand on a phosphadiazonium Lewis acceptor. As such, the complex ions [MesNP.L](+) are novel examples of cationic systems containing dicoordinate phosphorus centers. The complexes highlight the potential for electron-rich centers to behave as Lewis acids despite the presence of a lone pair of electrons at the acceptor site.

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PubMed2003

A reversible valence equilibrium in a heavier main group compound.

The addition of LiPh to Ar*SnCl (Ar* = C6H3-2,6-Trip2; Trip = C6H2-2,4,6-iPr3) at low temperature afforded the Sn(1)-Sn(III) species Ar*SnSnPh2Ar*, which exists in equilibrium with the Sn(II) compound Ar*SnPh. It is the first example of a room-temperature equilibrium of compounds involving main group elements in different oxidation states.

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PubMed2003

Structures, bonding, and reaction chemistry of the neutral organogallium(I) compounds (GaAr)n(n = 1 or 2) (Ar = terphenyl or related ligand): an experimental investigation of Ga-Ga multiple bonding.

The synthesis, structure, and properties of several new organogallium(I) compounds are reported. The monovalent compounds GaAr* (Ar* = C(6)H(3)-2,6-Trip(2), Trip = C(6)H(2)-2,4,6-Pr(i)()(3), 1), GaAr# (Ar# = C(6)H(3)-2,6(Bu(t)Dipp)(2), Bu(t)Dipp = C(6)H(2)-2,6-Pr(i)(2)-4-Bu(t)(), 4), and the dimeric (GaAr')(2) (Ar' = C(6)H(3)-2,6-Dipp(2), Dipp = C(6)H(3)-2,6-Pr(i)(2), 6) were synthesized by the reaction of "GaI" with (Et(2)O)LiAr*, (Et(2)O)LiAr# (3), or (LiAr')(2). Compounds 1 and 4 were isolated as green crystals, whereas 6 was obtained as a brown-red crystalline solid. All three compounds dissolved in hydrocarbon solvents to give green solutions and almost identical UV/visible spectra. Cryoscopy of 1 and 6 showed that they were monomeric in cyclohexane. Crystals of 1 and 4 were unsuitable for X-ray crystal structure determinations, but an X-ray data set for 6 showed that it was weakly dimerized in the solid with a long Ga-Ga bond of 2.6268(7) A and a trans-bent CGaGaC core array. The 1,2-diiodo-1,2-diaryldigallane compounds [Ga(Ar*)I](2) (2), [Ga(Ar#)I](2) (5), and [Ga(Ar')I](2) (7) were isolated as byproducts of the synthesis of 1, 4, and 6. The crystal structures of 2 and 7 showed that they had planar ICGaGaCI core arrays with Ga-Ga distances near 2.49 A, consistent with Ga-Ga single bonding. Treatment of 1, 4, and 6 with B(C(6)F(5))(3) immediately afforded the 1:1 donor-acceptor complexes ArGa[B(C(6)F(5))(3)] (Ar = Ar*, 8; Ar#, 9; Ar', 10) that featured almost linear gallium coordination, Ga-B distances near the sum of the covalent radii of gallium and boron, as well as some close Ga...F contacts. Compound 1 also reacted with Fe(CO)(5) under ambient conditions to give Ar*GaFe(CO)(4) (11), which had been previously synthesized by the reaction of GaAr*Cl(2) with Na(2)Fe(CO)(4). Reaction of 1 with 2,3-dimethyl-1,3-butadiene afforded the compound [Ar*GaCH(2)C(Me)C(Me)CH(2)]2 (12) that had a 10-membered 1,5-Ga(2)C(8) ring with no Ga-Ga interaction. Stirring 1 or 6 with sodium readily gave Na(2)[Ar*GaGaAr*] (13) and Na(2)(Ar'GaGaAr') (14). The former species 13 had been synthesized previously by reduction of GaAr*Cl(2) with sodium and was described as having a Ga-Ga triple bond because of the short Ga-Ga distance and the electronic relationship between [Ar*GaGaAr*](2-) and the corresponding neutral group 14 alkyne analogues. Compound 14 has a similar structure featuring a trans-bent CGaGaC core, bridged by sodiums which were also coordinated to the flanking aryl rings of the Ar' ligands. The Ga-Ga bond length was found to be 2.347(1) A, which is slightly (ca. 0.02 A) longer than that reported for 13. Reaction of Ga[N(Dipp)C(Me)](2)CH, 15 (i.e., GaN(wedge)NDipp(2)), which is sterically related to 1, 4, and 6, with Fe(CO)(5) yielded Dipp(2)N(wedge)NGaFe(CO)(4) (16), whose Ga-Fe bond is slightly longer than that observed in 11. Reaction of the less bulky LiAr"(Ar"= C(6)H(3)-2,6-Mes(2)) with "GaI" afforded the new paramagnetic cluster Ga(11)Ar(4)" (17). The ready dissociation of 1, 4, and 6 in solution, the long Ga-Ga distance in 6, and the chemistry of these compounds showed that the Ga-Ga bonds are significantly weaker than single bonds. The reduction of 1 and 6 with sodium to give 13 and 14 supplies two electrons to the di-gallium unit to generate a single bond (in addition to the weak interaction in the neutral precursor) with retention of the trans-bent geometry. It was concluded that the stability of 13 and 14 depends on the matching size of the sodium ion, and the presence of Na-Ga and Na-Ar interactions that stabilize their Na(2)Ga(2) core structures.

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PubMed2003

Nitrogen ligands on phosphorus(III) Lewis acceptors: A versatile new synthetic approach to unusual N-P structural arrangements.

A series of Lewis acid-base adducts of phosphines with amines or pyridines have been prepared and structurally characterized, demonstrating the importance of Lewis acceptor behavior in the chemistry of electron-rich (lone-pair-bearing) centers. The neutral and cationic complexes all contain examples of N-P coordinate bonds that are void of N-P pi-bonding and therefore represent definitive N-P single bonds. The structures are examples of N-P topologies that are rare or have not previously been observed, highlighting the synthetic viability of Lewis acid-base coupling in the still developing field of nitrogen-phosphorus chemistry.

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PubMed2003

Synthesis and characterization of the monomeric imides Ar'MNAr' ' (M = Ga or In; Ar' or Ar' ' = terphenyl ligands) with two-coordinate gallium and indium.

Reaction of Ar'MMAr' (M = Ga or In) with N3Ar' ' (Ar' = C6H3-2,6-Dipp2, Dipp = C6H3-2,6-Pri2, Ar' ' = C6H3-2,6(Xyl-4-But)2) afforded the first monomeric imides of heavier group 13 elements with two-coordinate metals. Planar, trans-bent structures with short M-N bond distances were observed, which are consistent with lone pair character at both M and N and a bond order less than the formally expected triple one.

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PubMed2003

Human Gene Mutation Database (HGMD): 2003 update.

The Human Gene Mutation Database (HGMD) constitutes a comprehensive core collection of data on germ-line mutations in nuclear genes underlying or associated with human inherited disease (www.hgmd.org). Data catalogued includes: single base-pair substitutions in coding, regulatory and splicing-relevant regions; micro-deletions and micro-insertions; indels; triplet repeat expansions as well as gross deletions; insertions; duplications; and complex rearrangements. Each mutation is entered into HGMD only once in order to avoid confusion between recurrent and identical-by-descent lesions. By March 2003, the database contained in excess of 39,415 different lesions detected in 1,516 different nuclear genes, with new entries currently accumulating at a rate exceeding 5,000 per annum. Since its inception, HGMD has been expanded to include cDNA reference sequences for more than 87% of listed genes, splice junction sequences, disease-associated and functional polymorphisms, as well as links to data present in publicly available online locus-specific mutation databases. Although HGMD has recently entered into a licensing agreement with Celera Genomics (Rockville, MD), mutation data will continue to be made freely available via the Internet.

Databases, Genetic↗