LATE TRANSITION-METAL SULFIDO COMPLEXES - REACTIVITY STUDIES AND MECHANISTIC ANALYSIS OF THEIR CONVERSION INTO METAL-SULFUR CUBANE COMPLEXES

Bimetallic bridging sulfur complexes having the general structure CpM (PR(3))S(2)IrCp (3, R = Me, M = Ir; 12, R = Me, M = Rh; 15, R = p-tol yl, M = Lr) have been prepared. Heating these compounds leads to the m etalla-sulfur cubane complexes (CpMS)(2)(Cp*IrS)(2) (10, M = Ir; 13, M = Rh). The observation that diiridium/dirhodium complex 13 is the on ly product obtained quantitatively from the thermolysis of 12 provides evidence that the dimeric units remain intact on the pathway to cuban e formation rather than dissociating to monomeric units followed by re assembly into the tetramer. A mechanistic study of the cubane-assembly reaction was undertaken using complex 15. The reaction is first-order in [15] and zero-order in [PR(3)] when the concentration of phosphine is low. At high (flooding) [PR(3)], the rate is second-order in [15] and inverse second-order in phosphine concentration. These data are co nsistent with a mechanism in which a doubly unsaturated intermediate, CpMS(2)-IrCp*, is generated by reversible loss of phosphine and then in a second bimolecular step dimerizes to form the cubane. The reactio ns of 3 with methyl bromide, carbon monoxide, and tert-butyl isocyanid e are also described. The single crystal X-ray structures of CpIr(PMe (3))S(2)IrCp (3), Cp*Ir(CN-t-Bu)(mu-S)(2)Ir(CN-t-Bu)Cp* (9), and (Cp* IrS)(4) (10) have been determined. Complex 3 crystallized in the monoc linic system, space group P2(1) with a 8.556(1) Angstrom, b = 14.093(2 ) Angstrom, c = 10.977(2) Angstrom, beta = 103.28(1)degrees, and Z = 2 . Refinement by standard least-squares techniques gave final residuals R = 0.039 and R(W) = 0.040. Complex 9 crystallized in the monoclinic system, space group C2/c with a = 18.798(5) Angstrom, b = 9.554(2) Ang strom, c = 18.219(3) Angstrom, beta = 90.34 degrees, and Z = 8. Refine ment by standard least-squares techniques gave final residuals R = 0.0 34 and R(W) = 0.040. Complex 10 crystallized in the orthorhombic syste m, space group I ($) over bar 4 with a = 12.026(3) Angstrom, b = 12.02 6(3) Angstrom, c = 14.844(3) Angstrom, and Z = 2. Refinement by standa rd least squares techniques gave final residuals R = 0.031 and R(W) = 0.039.