SYNTHESIS AND REACTION CHEMISTRY OF SOME MULTIPLY BONDED COMPLEXES OF DIOSMIUM: ISOCYANIDE CHEMISTRY OF OSMIUM AND RUTHENIUM
Abstract
The triply bonded octahalodiosmate(III) anions Os(,2)X(,8) ('2-) (X = Cl, Br) are formed by the reactions of Os(,2)(O(,2)CCH(,3))(,4)Cl(,2) with gaseous HX in ethanol. These green diamagnetic species possess extremely short osmium-osmium distances ((TURN)2.18(ANGSTROM)) and have twist angles which vary from 0.0(DEGREES) for the brown form of the (Ph(,3)P)(,2)N ('+) salt (X = Cl) to approximately 45(DEGREES) for the n-Bu(,4)N ('+) salts (X = Cl, Br). A second crystalline form of (Ph(,3)P)(,2)N (,2)Os(,2)Cl(,8) has also been isolated which displays two different rotational geometries for the major and minor orientations (X = 11.4 and 39.8(DEGREES), respectively). The electronic configuration of the osmium-osmium bond in these anions is believed to be (sigma)('2)(pi)('4)(delta)('2)(delta)('*2); this configuration imposes no electronic barrier to rotation in these complexes which is reflected in the crystal structures obtained. The reaction chemistry of these Os(,2)X(,8) ('2-) anions with monodentate phosphines, isocyanides, and carbon monoxide has been investigated. These ligands initially react by cleaving the osmium-osmium bond with subsequent formation of the trans- OsX(,4)L(,2) ('-) anions. Some of these anions were isolated and their spectroscopic and electrochemical properties were investigated. The reaction chemistry of these anions with excess ligand was also investigated. While the CO and RNC (R = CMe(,3), 2,6-xylyl) derivatives were unreactive, the phosphine-containing species trans- OsX(,4)(PR(,3))(,2) ('-) react readily with excess phosphine to generate several different osmium(II) and osmium(III) halide-phosphine complexes. The electrochemical properties of the diosmium(III) complexes Os(,2)(O(,2)CR)(,4)X(,2) (X = Cl, Br; R = Et, n-Pr) and Os(,2)(hp)(,4)Cl(,2) reveal that each of them possess a reversible one-electron reduction. These reductions can also be performed chemically using cobaltocene as reductant. These complexes are the first reported derivatives containing Os(,2)('5+) cores and have been characterized by cyclic voltammetry, electronic absorption and ESR spectroscopy, and magnetic susceptibility measurements. These complexes are believed to contain Os-Os multiple bonds of order 2.5 with the configurations (sigma)('2)(pi)('4)(delta)('2)(delta)('*1)(pi)('*2) (S = 3/2) and (sigma)('2)(pi)('4)(delta)('2)(delta)('*1)(pi)('*1) and/or (sigma)('2)(pi)('4)(delta)('2)(pi)('*3) (S = 1/2) being the principal contributors to the ground state at room temperature. Alkyl isocyanides RNC (R = CMe(,3), CHMe(,2), C(,6)H(,11)) react with Ru(,2)(O(,2)-CCH(,3))(,4)Cl and Os(,2)(O(,2)CCH(,3))(,4)Cl(,2) to give the homoleptic metal(II) complexes M(CNR)(,6) (PF(,6))(,2).
Degree
Ph.D.
Subject Area
Chemistry
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