Bis(diphenylphosphino)methane Induces Unusual Cyclometalation of Thiophene and Phenyl Rings (R) at the C² Carbon of Thiosemicarbazones {R-C²(H) = N³-N² H-C(═S)-N¹H₂} in Ruthenium(II) Complexes

Abstract

Reaction of trans-[Ru(dppm)2Cl2] (dppm = Ph2PCH2PPh2) with thiophene-2-carbaldehyde thiosemicarbazone {C4H3S-C2(H)═N3-N2H-C1(═S)-N1H2, H2L1} in the presence of Et3N base formed a complex, [Ru(η3-C,N3,S-L1)(η2-P,P-dppm)(η1-P-dppm)] (1) (L1 is dinegative thiophene-2-carbaldehyde thiosemicarbazonate), with an unprecedented cyclometalation of a heterocyclic ring in RuII-thiosemicarbazone chemistry. In contrast, the thiophene ring did not undergo cyclometalation in complexes of monotertiary phosphines of stoichiometry [Ru(η2-N2,S-HL1)2(PR′3)2] (R′ = phenyl, 2; p-tolyl, 3; HL1 = uninegative thiophene-2-carbaldehyde thiosemicarbazonate). Benzaldehyde thiosemicarbazone {C6H5-C(H)═N3-N2H-C(═S)-N1H2,H2L2} with trans-[Ru(dppm)2Cl2] displayed cyclometalation and yielded an organometallic complex [Ru(η3-C,N3,S-L2)(η2-P,P-dppm)(η1-P-dppm)] (4) (L2 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 η1-P-dppm and chelating η2-P,P-dppm in the same complex. These cyclometalation reactions represent the first examples in RuII-thiosemicarbazone chemistry.