The Square Pyramidal Hydride Cation [RuH(dcpe)2]+, dcpe = Bis(dicyclohexylphosphino)ethane. Structures of [RuH(dcpe)2]+[BPh4]- and of the Zwitterionic {(η6-C6H5)BPh3}RuH(dcpe)

Abstract

Two hydrido ruthenium complexes could be isolated from the reaction between RuCl2(DMSO)4 (DMSO = dimethyl sulfoxide) and the chelating 1,2-bis(dicyclohexylphosphino)ethane (dcpe) and [BPh4]-. These are [RuH(dcpe)2]+[BPh4]- with a five-coordinate, 16 valence electron cation and the neutral zwitterionic 18 valence electron compound {(η6-C6H5)BPh3}RuH(dcpe). The relative amounts of these products depend on the reaction conditions. If NaBPh4 is replaced by NH4PF6 or added after the reaction with the diphosphine has gone to completion, the 16 valence electron species [RuH(dcpe)2]+ is the only product. Reducing the size of the diphosphine chelate to 1,1-bis(dicyclohexylphosphino)methane (dcpm) has a large effect on the reaction course. Either trans-RuHCl(dcpm)2 or trans-RuCl2(dcpm)2 is formed, depending on the conditions. X-ray structures of [RuH(dcpe)2]+[BPh4]- (monoclinic, P2/c, a = 24.936(5) Å, b = 12.633(3) Å, c = 25.801(5) Å, β = 102.86(3)°, V = 7924(3) Å3, Z = 4, R = 0.062, Rw = 0.1694) and {(η6-C6H5)BPh3}RuH(dcpe) (monoclinic, P21/n, a = 14.321(5) Å, b = 19.716(7) Å, c = 17.100(5) Å, β = 107.60°, V = 4602(3) Å3, Z = 4, R = 0.0648, Rw = 0.1873) have been determined. A nearly planar arrangement of the four P atoms exists around Ru in the five-coordinate cation, implying a distorted square pyramid. This structural motif has not been observed previously for a d6 RuL5 system with a P4X donor set. {(η6-C6H5)BPh3}RuH(dcpe) represents an example for the noninnocent behavior of the “noncoordinating” [BPh4]- anion. The coordinated six-membered ring displays a boatlike distortion with the BPh3 “substituent” and the para-carbon of the coordinated ring displaced away from the metal.