Addition of E−H Bonds (E = S, N) across the CαCβ Bond of the Allenylidene Ligand in [Re{CCCPh2}(CO)2(triphos)](OSO2CF3) (Triphos = MeC(CH2PPh2)3)

Abstract

Reaction of the rhenium(I) allenylidene complex [Re{CCCPh2}(CO)2(triphos)]OTf (1; triphos = MeC(CH2PPh2)3, OTf = -OSO2CF3) with thiophenol, 2-thionaphthol, or allyl mercaptan gave selectively the α,β-unsaturated thiocarbene complexes [Re{C(SR)CHCPh2}(CO)2(triphos)]OTf (R = Ph (2), α-naphthyl (3), CH2CHCH2 (4)). A reversible reaction was observed for PhSH in DMSO at 80 °C. Compounds 2 and 3 have been found to react with sodium alkoxides, yielding the kinetic thioallenyl products [Re{C(SR)CCPh2}(CO)2(triphos)] (R = Ph (6a), α-naphthyl (7a)). These equilibrated in room-temperature solution with the thermodynamic thioalkynyl products [Re{C⋮CC(SR)Ph2}(CO)2(triphos)] (R = Ph (6b), α-naphthyl (7b)) to give stationary states (6a/6b, 40/60; 7a/7b, 20/80). Deprotonation of the thioallyl complex 4 gave the stable allenyl derivative [Re{C(SCH2CHCH2)CCPh2}(CO)2(triphos)] (8). Ammonia, aniline, and propargylamine each reacted with 1 to give the azoniabutadienyl compounds [Re{C(NHR)CHCPh2}(CO)2(triphos)]OTf (R = H (9), Ph (10), CH2C⋮CH (11)) via N−H bond addition across the CαCβ double bond. NMR spectroscopy showed the γ-alkynylammonium complex [Re{C⋮CCPh2(NH3)}(CO)2(triphos)]OTf (12) to be a transient intermediate along the reaction of 1 with ammonia. Treatment of 10 or 11 with sodium methoxide resulted in the selective deprotonation of the nitrogen atom to give the azabutadienyl compounds [Re{C(NR)CHCPh2}(CO)2(triphos)] (R = Ph (13), CH2C⋮CH (14)). The molecular structure of the azoniabutadienyl complex 11 was determined by a single-crystal X-ray analysis. The geometry around the rhenium center conforms to a slightly distorted octahedron, with the polyphosphine sitting on a face of the coordination polyhedron. In keeping with the azoniabutadienyl structure, the Re−Cα bond length is 2.151(7) Å, and the Cα−N distance is 1.300(9) Å.