η 1 ‐Coordination of Phosphinine C 5 H 5 P and Arsenine C 5 H 5 As to Ruthenium(II) and Osmium(II)

Reductive complexation of RuCl 3 and OsCl 3 in the presence of phosphinine C 5 H 5 P and arsenine C 5 H 5 As yields the species trans ‐Cl 2 (η 1 ‐C 5 H 5 E) 4 M II (M = Ru, E = P, As; M = Os, E = P). trans ‐Cl 2 (η 1 ‐C 5 H 5 As) 4 Ru constitutes the first arsenine complex of a late transition metal. Further reduction and isolation of the binary complexes (C 5 H 5 E) n M 0 ( n = 2, 4, 5) failed, presumably because of metal–ligand bond cleavage. According to X‐ray diffraction analysis, trans ‐Cl 2 (η 1 ‐C 5 H 5 P) 4 Ru ( 3 ) features two pairs of coplanar trans ‐phosphinine ligands, which adopt eclipsed and staggered orientations, respectively, with regard to the Cl–Ru–Cl backbone. DFT calculations indicate a flat curvature of the potential governing conformational change and predict a structure for 3 that differs from that observed in the crystal. This illustrates the need to include intermolecular Ru–Cl ··· H hydrogen bonding as a structural director. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)