Biomedical subjects

John C. Jeffery

Publications and source records attributed to John C. Jeffery.

6 recordsLinked to original sources

PubMed1999

The Reagent [K(18-crown-6)][RuH(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))] as a Precursor to New Ruthenacarborane Complexes.

In ethanol the charge-compensated molecule exo-nido-ruthenacarborane [5,6,10-{RuCl(PPh(3))(2)}-5,6,10-&mgr;-(H)(3)-10-H-7,8-C(2)B(9)H(8)] reacts with KOH to afford the anionic closo-complex [RuH(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))](-) isolated as its K(+) (2a) or [K(18-crown-6)](+) (2b) salt. Treatment of 2a with CO gives [Ru(CO)(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))] (3a) in high yield; its structure was determined by X-ray crystallography. In contrast 2b reacts with CO to yield the salt [K(18-crown-6)][RuH(CO)(PPh(3))(eta(5)-7,8-C(2)B(9)H(11))] (2d). Reaction of 2b with [RuCl(2)(PPh(3))(3)] affords [Ru(2)(&mgr;-H)(H)(PPh(3))(4)(eta(5)-7,8-C(2)B(9)H(11))] (5), which with CO produces [Ru(2)(&mgr;-H)(&mgr;-sigma: eta(5)-7,8-C(2)B(9)H(10))(CO)(4)(PPh(3))(2)] (6), the structure of which was established by X-ray diffraction. The molecule has a metal-metal bond bridged on one side by a hydrido ligand and on the other by a nido-7,8-C(2)B(9)H(10) fragment. The latter is eta(5)-coordinated to a ruthenium atom ligated by a PPh(3) and a CO ligand and is also sigma-bonded to the second ruthenium which carries three CO molecules and a PPh(3) group. The sigma bond utilizes a boron lying in an alpha site with respect to the carbons in the ring coordinated to the Ru(CO)(PPh(3)) moiety. Reactions between 2b or 2d and [CuCl(PPh(3))(3)] and [AuCl(PPh(3))], respectively, afford the bimetal complexes [RuM(&mgr;-H)(L)(PPh(3))(2)(eta(5)-7,8-C(2)B(9)H(11))] [M = Cu, L = PPh(3) (7a), L = CO (7b); M = Au, L = PPh(3) (8a), L = CO (8b)]. X-ray diffraction studies are reported for 7a and 8a, revealing in the case of the former a structure in which an exopolyhedral B-Hright harpoon-up Cu bond supplements the Ru(&mgr;-H)Cu interaction.

Journal Article↗

PubMed1997

Roles of Bridging Ligand Topology and Conformation in Controlling Exchange Interactions between Paramagnetic Molybdenum Fragments in Dinuclear and Trinuclear Complexes.

The magnetic properties of two series of dinuclear complexes, and one trinuclear complex, have been examined as a function of the bridging pathway between the metal centers. The first series of dinuclear complexes is [{Mo(V)(O)(Tp)Cl}(2)(&mgr;-OO)], where "OO" is [1,4-O(C(6)H(4))(n)O](2)(-) (n = 1, 1; n = 2, 3), [4,4'-O(C(6)H(3)-2-Me)(2)O](2)(-) (4), or [1,3-OC(6)H(4)O](2)(-) (2) [Tp = tris(3,5-dimethylpyrazolyl)hydroborate]. The second series of dinuclear complexes is [{Mo(I)(NO)(Tp)Cl}(2)(&mgr;-NN)], where "NN" is 4,4'-bipyridyl (5), 3,3'-dimethyl-4,4'-bipyridine (6), 3,8-phenanthroline (7), or 2,7-diazapyrene (8). The trinuclear complex is [{Mo(V)(O)(Tp)Cl}(3)(1,3,5-C(6)H(3)O(3))] (9), whose crystal structure was determined [9.5CH(2)Cl(2): C(56)H(81)B(3)Cl(13)Mo(3)N(18)O(6); monoclinic, P2(1)/n; a = 13.443, b = 41.46(2), c = 14.314(6) Å; beta = 93.21(3) degrees; V = 7995(5) Å(3); Z = 4; R(1) = 0.106]. In these complexes, the sign and magnitude of the exchange coupling constant J is clearly related to both the topology and the conformation of the bridging ligand [where J is derived from H = -JS(1)().S(2)() for 1-8 and H = -J(S(1)().S(2)() + S(2)().S(3)() + S(1)().S(3)()) for 9]. The values are as follows: 1, -80 cm(-)(1); 2, +9.8 cm(-)(1); 3, -13.2 cm(-)(1); 4, -2.8 cm(-)(1); 5, -33 cm(-)(1); 6, -3.5 cm(-)(1); 7, -35.6 cm(-)(1); 8, -35.0 cm(-)(1); 9, +14.4 cm(-)(1). In particular the following holds: (1) J is negative (antiferromagnetic exchange) across the para-substituted bridges ligands of 1 and 3-8 but positive (ferromagnetic exchange) across the meta-substituted bridging ligands of 2 and 9. (2) J decreases in magnitude dramatically as the bridging ligand conformation changes from planar to twisted (compare 3 and 4, or 6 and 8). These observations are consistent with a spin-polarization mechanism for the exchange interaction, propagated across the pi-system of the bridging ligand by via overlap of bridging ligand p(pi) orbitals with the d(pi) magnetic orbitals of the metals. The EPR spectrum of 9 is characteristic of a quartet species and shows weak Deltam(s) = 2 and Deltam(s) = 3 transitions at one-half and one-third, respectively, of the field strength of the principal Deltam(s) = 1 component.

Journal Article↗

PubMed1997

Large Molecular Quadratic Hyperpolarizabilities in Donor/Acceptor-Substituted trans-Tetraammineruthenium(II) Complexes.

A series of new Ru(II) complex salts trans-[Ru(NH(3))(4)(L(1))(L(2))](PF(6))(n) [n = 2, L(1) = 4-acetylpyridine (4-acpy) and L(2) = 4-(dimethylamino)pyridine (dmap) (1), 4-(dimethylamino)benzonitrile (dmabn) (2), 4-picoline (4-pic) (3), or 1-methylimidazole (1-MeIm) (4); n = 3, L(1) = N-methyl-4,4'-bipyridinium (MeQ(+)) and L(2) = dmap (6), dmabn (7), 1-MeIm (8), 4-acpy (9), or phenothiazine (PTZ) (10); n = 2, L(1) = dmap and L(2) = 4-pyridinecarboxaldehyde (pyca) (12) or ethyl isonicotinate (isne) (13)] have been synthesized and fully characterized. These complexes display intense, visible metal-to-ligand charge-transfer (MLCT) absorptions which are highly solvatochromic. An X-ray crystal structure determination has been carried out for trans-[Ru(NH(3))(4)(MeQ(+))(PTZ)](PF(6))(3).Me(2)CO (10.Me(2)CO). This salt, empirical formula C(26)H(38)F(18)N(7)OP(3)RuS, crystallizes in the hexagonal system, space group P6(3), with a = b = 17.853(4) Å, c = 21.514(6) Å, and Z = 6. The MeQ(+) ligand adopts an almost planar conformation, with a torsion angle of 9.6 degrees between the two pyridyl rings. The dipolar cations exhibit a strong projected component along the z axis, but crystal twinning precludes second-harmonic generation. Measurements of the first hyperpolarizability beta by using the hyper-Rayleigh scattering technique at 1064 nm yield very large values in the range (232-621) x 10(-30) esu, the largest being for trans-[Ru(NH(3))(4)(MeQ(+))(dmabn)](PF(6))(3) (7). These beta values are resonance enhanced via the MLCT excitations. A correlation between beta and the MLCT absorption energy confirms that this excitation is the primary contributor to beta. The two-level model yields static hyperpolarizabilities beta(0) in the range (10-130) x 10(-30) esu, with trans-[Ru(NH(3))(4)(MeQ(+))(dmap)](PF(6))(3) (6) having the largest. The beta(0) values of the complexes of the bipyridyl ligand MeQ(+) are larger than those of their analogues containing monopyridyl ligands because of extended conjugation. beta(0) correlates with the MLCT energy only when the MLCT absorption is sufficiently far from the second harmonic at 532 nm.

Journal Article↗

PubMed1997

A Triangular Copper(I) Complex Displaying Allosteric Cooperativity in Its Electrochemical Behavior and a Mixed-Valence Cu(I)-Cu(I)-Cu(II) State with Unusual Temperature-Dependent Behavior.

Reaction of the tris-chelating hexadentate podand ligand tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (Tp(Py)) with [Cu(MeCN)(4)][PF(6)] affords [Cu(I)(3)(Tp(Py))(2)][PF(6)] (1), which was crystallographically characterized. 1.(MeCN)(2): C(52)H(44)B(2)Cu(3)F(6)N(20)P, orthorhombic, Pna2(1); a = 24.592(7), b = 16.392(5), c = 13.365(5) Å; Z = 4. Each Cu(I) ion is four coordinated by one N,N '-bidentate arm from each ligand; each ligand therefore donates each bidentate arm to a different Cu(I) ion. The isosceles triangular arrangement of Cu(I) ions with N-donor ligands is reminiscent of the tricopper(I) site of ascorbate oxidase. One-electron oxidation of 1 affords the Cu(I)(2)Cu(II) complex [Cu(3)(Tp(Py))(2)][PF(6)](2) (2). The potentials of the Cu(I)/Cu(II) redox couples are affected by the ease with which the accompanying geometric rearrangement can occur. Thus, the first oxidation of 1 is facile (-0.52 V vs the ferrocene/ferrocenium couple, Fc/Fc(+)), but as a result of the concomitant structural rearrangement the second oxidation is rendered much more difficult (+0.12 V vsFc/Fc(+)) and results in slow decomposition of the product. A third oxidation does not occur at accessible potentials. This complex therefore exhibits negative cooperative behavior, in which the geometric change accompanying one metal-based redox change hinders further redox changes at other sites via an allosteric effect. EPR studies on the mixed-valence complex 2 show that in frozen glasses below 120 K the unpaired electron is delocalized over two metal centers (7-line spectrum), but above 160 K the electron becomes localized and gives a simple axial spectrum. The electronic spectrum of 2 in solution shows an intense band at 910 nm (epsilon 2100 dm(3) mol(-)(1) cm(-)(1)) which we believe to be an IVCT band. The combination of EPR and electronic spectral studies show that 2 is class III (fully delocalized over 2 centers) below 120 K but class II (localized but strongly interacting) at higher temperatures.

Journal Article↗

PubMed1997

Template Synthesis and Reactions of Tricarbonylmolybdenum Phosphadithiamacrocycle Complexes.

Treatment of [Me(4)N](2)[PhP(CH(2)CH(2)S)(2)] with [Mo(CO)(3)(NCMe)(3)] affords the reactive intermediate [Me(4)N](2)[Mo(CO)(3){PhP(CH(2)CH(2)S)(2)}] (1), which undergoes oxidation to afford [Mo{PhP(CH(2)CH(2)S)(2)}(2)] (2). Reaction of 1 with a variety of dichloroalkanes produces [Mo(CO)(3){c-PhP(CH(2)CH(2)S)(2)X}] (X = CH(2)CH(2), CH(2)CH(2)CH(2), CH(2)CHMe or CH(2)CH(OH)CH(2)). The structure of [Mo(CO)(3){c-PhP(CH(2)CH(2)S)(2)CH(2)CH(2)}] (3) has been established by X-ray crystallography and consists of a Mo(CO)(3) fragment facially coordinated by the tridentate c-PhP(CH(2)CH(2)S)(2)CH(2)CH(2) ligand. Reaction of 3 with bromine affords seven-coordinate [Mo(CO)(2){c-PhP(CH(2)CH(2)S)(2)CH(2)CH(2)}Br(2)] (7), the X-ray crystal structure of which reveals a carbonyl-capped octahedral geometry. Treatment of 3 with sulfur results in loss of the Mo(CO)(3) fragment and isolation of c-PhPS(CH(2)CH(2)S)(2)CH(2)CH(2) (8), the X-ray structure of which shows a nine-membered ring with the phosphorus center bearing phenyl and sulfide substituents. Reduction of 8 with sodium naphthalenide affords the parent ligand c-PhP(CH(2)CH(2)S)(2)CH(2)CH(2). Crystal data: 2, C(20)H(26)MoP(2)S(4), triclinic P&onemacr;, a = 8.105(3) Å, b = 8.263(3) Å, c = 17.663(4) Å, alpha = 100.29(2) degrees, beta = 99.78(2) degrees, gamma = 98.81(2) degrees, Z = 2; 3, C(15)H(17)MoO(3)PS(2), monoclinic P2(1)/n, a = 9.600(3) Å, b = 15.594(5) Å, c = 11.335(3) Å, beta = 93.01(2) degrees, Z = 4; 7, C(14)H(17)Br(2)MoO(2)PS(2), monoclinic P2(1)/c, a = 17.039(3) Å, b = 8.686(2) Å, c = 12.466(3) Å, beta = 100.52(2) degrees, Z = 4; 8, C(12)H(17)PS(3), monoclinic P2(1), a = 6.651(4) Å, b = 7.313(2) Å, c = 14.687(9) Å, beta = 101.62(3) degrees, Z = 2.

Journal Article↗

PubMed1996

Reaction of nido-7,8-C(2)B(9)H(13) with Dicobalt Octacarbonyl: Crystal Structures of the Complexes [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)], [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)], and [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))].

The compounds [Co(2)(CO)(8)] and nido-7,8-C(2)B(9)H(13) react in CH(2)Cl(2) to give a complex mixture of products consisting primarily of two isomers of the dicobalt species [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (1), together with small amounts of a mononuclear cobalt compound [Co(CO)(2)(eta(5)-10-CO-7,8-C(2)B(9)H(10))] (5) and a charge-compensated carborane nido-9-CO-7,8-C(2)B(9)H(11) (6). In solution, isomers 1a and 1b slowly equilibrate. However, column chromatography allows a clean separation of 1a from the mixture, and a single-crystal X-ray diffraction study revealed that each metal atom is ligated by a terminal CO molecule and in a pentahapto manner by a nido-C(2)B(9)H(11) cage framework. The two Co(CO)(eta(5)-7,8-C(2)B(9)H(11)) units are linked by a Co-Co bond [2.503(2) Å], which is supported by two three-center two-electron B-H right harpoon-up Co bonds. The latter employ B-H vertices in each cage which lie in alpha-sites with respect to the carbons in the CCBBB rings bonded to cobalt. Addition of PMe(2)Ph to a CH(2)Cl(2) solution of a mixture of the isomers 1, enriched in 1b, gave isomers of formulation [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)] (2). Crystals of one isomer were suitable for X-ray diffraction. The molecule 2a has a structure similar to that of 1a but differs in that whereas one B-H right harpoon-up Co bridge involves a boron atom in an alpha-site of a CCBBB ring coordinated to cobalt, the other uses a boron atom in the beta-site. Reaction between 1b and an excess of PMe(2)Ph in CH(2)Cl(2) gave the complex [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))] (3), the structure of which was established by X-ray diffraction. Experiments indicated that 3 was formed through a paramagnetic Co(II) species of formulation [Co(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))]. Addition of 2 molar equiv of CNBu(t) to solutions of either 1a or 1b gave a mixture of two isomers of the complex [Co(2)(CNBu(t))(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (4). NMR data for the new compounds are reported and discussed.

Journal Article↗