STRUCTURES AND FORMATION MECHANISM OF NOVEL METAL-CARBENE COMPLEXES DERIVED FROM HYPERVALENT THIADISELENADIAZAPENTALENES

ro-3,4-dimethylene-2,5-bis(4-chlorophenylimino)-6a lambda(4)-thia-1,6- diselena-3,4-diazapentalene (6), which contains a hypervalent sulfur a tom, has been found to give novel complexes by treating with [Pt(PPh3) (4)], [Pd(PPh3)(4)], and [RhCl(PPh3)(3)]. X-Ray investigations have re vealed that the resultant complexes are novel metal-carbene complexes: {1,1'-(perhydroimidazole-1,3-diyl-kappa to-kappa(2)SeSe']}(triphenylp hosphine)platinum(II) (8), {1,1'-(perhydroimidazole-1,3-diyl-kappa o-k appa(2)SeSe']}(triphenylphosphine)palladium(II) (9), and s(P,P')-(chlo ro){(perhydroimidazole-1,3-diyl-kappa kappa(2)SeSe']}bis(triphenylphos phine)rhodium(III) (10). The central sulfur atom in 6 was substituted by a metal atom to form metal-selenium bonds in the resultant metallap entalene framework. The structure of complex (11), obtained from thiat etraazapentalene-2,5-diselone with [Pd(PPh3)(3)], was also determined by an X-ray analysis. This complex was also a metal-carbene complex wi th a metallapentalene framework: {1,1'-(perhydropyrimidine-1,3-diyl-ka ppa o-kappa(2)SeSe']}(triphenylphosphine)palladium(II) (11). The final R values are 0.038, 0.034, 0.046, and 0.032 for the 4494, 4234, 3919, and 4451 observed reflections for 8, 9, 10, and 11, respectively. The fact that similar metal-carbene complexes with a metallapentalene fra mework were obtained from both thiadiselenadiazapentalenes and thiatet raazapentalene-2,5-dithione/diselones confirms the previously proposed formation mechanism of these metal-carbene complexes.