Bis(diphenylphosphino)methane induces unusual cyclometalation of thiophene and phenyl rings (R) at the C2 carbon of thiosemicarbazones {R-C2(H) = N3-N2H-C(=S)-N1H2} in ruthenium(II) complexes

Reaction of trans-[Ru(dppm)(2)Cl-2] (dppm = Ph2PCH2PPh2) with thiophene-2-carbaldehyde thiosemicarbazone {C4H3S-C-2(H)=N-3-(NH)-H-2-C-1(=S)-(NH2)-H-1, H2L1) in the presence of Et3N base formed a complex, [Ru(eta(3)-C,N-3, S-L-1)(eta(2)-P,P-dppm)(eta(1)-P-dppm)] (1) (L-1 is dinegative thiophene-2-carbaidehyde thiosemicarbazonate), with an unprecedented cyclometalation of a heterocyclic ring in Ru-II-thiosernicarbazone chemistry. In contrast, the thiophene ring did not undergo cyclometalation in complexes of monotertiary phosphines of stoichiometry [Ru(eta(2)-N-2,S-HL1)2(PR'(3))(2)] (R' = phenyl, 2; p-tolyl, 3; HL1 = uninegative thiophene-2-carbaldehyde thiosemicarbazonate). Benzaldehyde thiosemicarbazone {C6H5-C(H)=N-3-(NH)-H-2-C(=S)-(NH2)-H-1,H2L2} with trans-[Ru(dppm)(2)Cl-2] displayed cyclometalation and yielded an organometallic complex [Ru(eta(3)-C,N-3, S-L-2)(eta(2)-P,P-dppm)(eta(1)-P-dppm)] (4) (L-2 is dinegative benzaldehyde thiosemicarbazonate), similar to complex 1. The complexes have been characterized using analytical, spectroscopic, and single-crystal X-ray crystallographic (1, 3, 4) studies. The cyclometalation in complexes 1 and 4 is attributed to the presence of two types of coordination modes of dppm, namely, both eta(1)-P-dppm and chelating eta(2)-P,P-dppm in the same complex. These cyclometalation reactions represent the first examples in Ru-II-wthiosemicarbazone chemistry.