Reactivity of Cationic Dinitrosyl Bisphosphine Rhenium Complexes toward Acetylene: Base-Controlled Product Formation

Reactions of the dinitrosyl bisphosphine rhenium cations [Re(NO)2(PR3)2][BArF 4] (R = Cy 1a; R = iPr 1b; [BArF 4]− = tetrakis[(3,5-bis(trifluoromethyl)phenyl)borate]) with acetylene yielded the alkynyl (o-vinyl)hydroxylamido nitrosyl bisphosphine complexes [Re(CHC(H)ONH)(CCH)(NO)(PR3)2][BArF 4] (3a and 3b) in the absence of base, while in the presence of 2,6-di(tert-butyl)pyridine formation of the neutral alkynyl complexes [Re(CCH)(NO)2(PR3)2] (4a and 4b) was observed. A plausible mechanism is presented and supported by various NMR techniques, IR spectroscopy, and DFT calculations. Treatment of 4a and 4b with [H(OEt2)2][BArF 4] gave the corresponding vinylidene complexes [Re(CCH2)(NO)2(PR3)2][BArF 4] (5a and 5b) in high yields, which only slowly convert into the alkynyl(o-vinyl)hydroxylamido nitrosyl bisphosphine complexes 3a and 3b when treated with a large excess of acetylene. Thiophenol or benzeneselenol underwent 1,2-additions onto the vinylidene ligands of 5a and 5b to yield the cationic Fischer-type carbene complexes [Re(C(XPh)CH3)(NO)2(PR3)2][BArF 4] (X = S 6a,b; X = Se 7a,b) quantitatively. X-ray diffraction studies were carried out on 4b, 5b, and 7a.