Studies of the insertion of an organic isothiocyanate into a rhenium-rhenium single bond and a new mode of metal-promoted coupling of isothiocyanates

Five new compounds were obtained from the reaction of Re-2(CO)(9)(MeCN) with EtO(2)-CN=C=S in a hexane solution at reflux (68 degrees C), These were identified as Re(CO)(4)[s-trans-mu-C,S-EtO(2)CN=CS]Re(CO)(5) (2, 7% yield), Re(CO)(4)[mu-C,S,N-EtO(2)CN=CS]Re(CO)(4) (3, 40% yield), Re(CO)(4)[mu-C,N,S-2-(EtO(2)C)(2)NC=NCS2]Re(CO)(4) (4, 17% yield), Re(CO)(4)[mu-C,N,S-2-(EtO(2)C)(2)NC=NCS2]Re(Co)(3)(NCMe) (5, 5% yield), and trace Re(CO)(4)[-C,N,S-2-(EtO(2)C)(H)-NC=NCS2]Re(CO)(4) (6), All five products have been characterized crystallographically. Compounds 2 and 3 can be described as dimetalated thioimidate complexes formed by the insertion of one EtO(2)CN=C=S molecule into the Re-Re bond of 1. Compounds 4 and 5 contain a (EtO(2)C)(2)NC=NCS2 ligand that was formed by the insertion and rearrangement of two isothiocyanate molecules in the Re-Re bond of 1. Compound 6 is similar to 5 but contains a bridging (EtO(2)C)(H)NC=NCS2 ligand instead. The reaction of Re(CO)(4)(PMe(2)Ph)Re(CO)(4)(NCMe) with EtO(2)CN=C=S yielded two isomeric products, trans-Re(CO)(4)(PMe(2)Ph)[mu-(EtO(2)C)N=CN(CO(2)Et)CS2]Re(CO)(4) (8) and cis-Re(CO)(4)(PMe(2)Ph)[mu-EtO(2)C)N=CN(CO(2)Et)CS2]Re(CO)(4) (9), plus a small amount of the dimetalated thioimidate compound Re-2(CO)(8)(PPhMe(2))(mu-EtO(2)CNCS) (10). Compounds 8 and 9 contain a bridging (EtO(2)C)N=CN(CO(2)Et)CS2 ligand that was also formed by the coupling and rearrangement of two isothiocyanate molecules, This ligand is considered to be an intermediate en route to the (EtO(2)C)(2)NC=NCS2 ligand as found in 4, since 8 and 9 can be transformed into the complex Re(CO)(4)[mu-C,N,S-2-(EtO(2)C)(2)NC=NCS2]Re(CO)(3)(PMe(2)Ph) (11), a phosphine derivative of 4, A small amount of the complex Re(CO)(3)(PPhMe(2))(mu-S2C=NCO(2)Et)Re(CO)(3)(PPhMe(2)) (12) was also formed from 8 and 9. Compound 12 contains a dithiocarbimato ligand in a novel tetradentate bridging coordination mode, A mechanism for the formation of the (EtO(2)C)(2)-NC=NCS2 ligand is presented and discussed.