Niobium And Tantalum Carbonyl And Alkyne Organometallic Complexes (dihaptoiminoacyl).
Real Obradors, Julio
1986
Abstract
Carbonyl complexes of formula CpMCl((mu)-Cl)(CO)(,2) (,2) (M = Nb (2), Ta (3)) were prepared by reduction of CpNbCl(,4) with aluminum powder in the presence of CO. The niobium complexes CpNbCl(,2)- (ArC(TBOND)CAr) (4) were prepared by the same route. Carbonyl com- plexes 2 and 3 reacted with diarylalkynes with loss of CO to afford the alkyne complexes 4 and CpTaCl(,2)(ArC(TBOND)CAr) (5) respectively. The oxy-chloro clusters CpNbCl((mu)-Cl) (,3)((mu)(,3)-O)((mu)(,3)-OH) (12b) and the isoelectronic CpNbCl((mu)-Cl) (,3)((mu)(,3)-O)((mu)(,3)-Cl) (12c) were obtained from 12a and fully characterized. In the triangulo clusters 12b and 12c there is a short distance (ca. 2.8(ANGSTROM)) between two of the Nb(IV) atoms indicating a single bond; the other two Nb(IV)-Nb(IV) distances are long (ca. 3.3(ANGSTROM)) and are considered nonbonding contacts. The Nb(III) complexes 2 and 4 are reduced with Na/Hg to give Nb(II) (d('3)-d('3)) diamagnetic dimers with bridging Cl ligands and a metal-metal single bond: Cp(,2)Nb(,2)(CO)(,4)((mu)-Cl)(,2) (6) and Cp(,2)Nb(,2)(ArCCAr)(,2)((mu)-Cl)(,2) (7). The structures of 6 and 7 are dramatically different. The alkyne complexes 4 and 5 reacted smoothly with MeLi to afford the corre- sponding dimethyl complexes CpM(Me)(,2)(ArC(TBOND)CAr) (M = Nb (8), Ta (9)). The dimethyl complex of Ta reated with tert-butylisonitrile, RNC, to form the (eta)('2)-alkyne, (eta)('2)-aminoacyl complex CpTa(Me)((eta)('2)-C(Me)N('t)Bu)(ArC(TBOND)CAr) (10). The ('13)C NMR chemical shift of the alkyne carbons in complexes 4, 5, 7, 8, 9, and 10 range from (delta)200 (in 10) to (delta)236 in 9, these low field shifts indicate that the alkynes act as 4 electron donors. In the crystallographically characterized alkyne complexes 4, 7 and 10 the metal-alkyne carbon distances are short (ranging from 2.063(5)(ANGSTROM) in 4 to 2.112(10)(ANGSTROM) in 10) and indicate M-C multiple bond character. The (eta)('2)-iminoacyl linkage in 10 is also strong, with Ta-C and Ta-N distances of 2.10(1) and 2.12(1)(ANGSTROM) respectively, indicating multiple M-C and M-N bond character. Complex 10 shows only one type of alkyne carbon resonance at (delta)199.7 down to -80 C, this is consistent with the structure only if there is fast rotation round the M-alkyne bond in the NMR time scale. Warming a solution of 10 to 60(DEGREES)C causes a quantitative conversion of the (eta)('2)-iminoacyl to the unusual metallacycle Cp(Me)TaCArCArCMeN('t)Bu, 11.(' )The pattern of bond length in 11 suggests that the metallacycle is best regarded as a derivative of a metallacyclopentatriene: 1-cyclopentadienyl-1,3-dimethyl-2-tert-butyl-4,5-diphenyl-1-tantala-2-aza-cyclopenta-1,3,5-triene. The relevant bond distances are: Ta-Me, 2.24(1);Ta-C(alpha), 1.98(1); Ta-N, 1.98(1); C(alpha)-C(beta), 1.48(2); C(beta)-C(beta)', 1.39(2); C(beta)'-N, 1.40(1)(ANGSTROM). The C(alpha) resonance occurs at (delta)231.6 and those for the C(beta) and C(beta)' (-C(Me)=C(Ph)-) occur at (delta)95.7 and (delta)121.5. The metallacycle is decidedly nonplanar; the angle between the C(alpha)-Ta-N and C-C-C-N planes is 119.5(DEGREES). (Abstract shortened with permission of author.)Subjects
Alkyne Carbonyl Complexes Dihaptoiminoacyl Niobium Organometallic Tantalum
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