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)

Two hydrido ruthenium complexes could be isolated from the reaction between RuCl 2 (DMSO) 4 (DMSO = dimethyl sulfoxide) and the chelating 1,2-bis(dicyclohexylphosphino)ethane (dcpe) and [BPh 4 ] - . These are [RuH(dcpe) 2 ] + [BPh 4 ] - with a five-coordinate, 16 valence electron cation and the neutral zwitterionic 18 valence electron compound {(η 6 -C 6 H 5 )BPh 3 }RuH(dcpe). The relative amounts of these products depend on the reaction conditions. If NaBPh 4 is replaced by NH 4 PF 6 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- RuCl 2 (dcpm) 2 is formed, depending on the conditions. X-ray structures of [RuH(dcpe) 2 ] + [BPh 4 ] - (monoclinic, P 2/ c, a = 24.936(5) Å, b = 12.633(3) Å, c = 25.801(5) Å, β = 102.86(3)°, V = 7924(3) Å 3, Z = 4, R = 0.062, R w = 0.1694) and {(η 6 -C 6 H 5 )BPh 3 }RuH(dcpe) (monoclinic, P 2 1 / n, a = 14.321(5) Å, b = 19.716(7) Å, c = 17.100(5) Å, β = 107.60°, V = 4602(3) Å 3, Z = 4, R = 0.0648, R w = 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 d 6 RuL 5 system with a P 4 X donor set. {(η 6 -C 6 H 5 )BPh 3 }RuH(dcpe) represents an example for the noninnocent behavior of the “noncoordinating” [BPh 4 ] - anion. The coordinated six-membered ring displays a boatlike distortion with the BPh 3 “substituent” and the para -carbon of the coordinated ring displaced away from the metal.