Chemistry of polynuclear allenyl complexes: The μ-η1 : η2-allenyl diruthenium system Ru2(CO)6(μ-PPh2)(μ-η1 :η2-C(Ph)CCH2). Dimetallocycles via CC, CN and CS bond forming reactions and the X-ray structure of Ru2(CO)6(μ-PPh2)[μ-η1 : η1-PhCC{C(EtS)N(H)tBu}CH2]