Synthesis of novel quadruply bridged M2Se4 clusters trans/anti and trans/syn-[(eta(5)-RC5H4)(2)M-2(mu-Se)(2)(mu-SeCH2Ph)(2)] (M = Mo, W) via an unexpected reaction of M equivalent to M triply bonded complexes [(eta(5)-RC5H4)(2)M-2(CO)(4)] with dibenzyl diselenide. Crystal structures of a pair of isomers trans/anti- and trans/syn-[(eta(5)-EtO2CC5H4)(2)Mo-2(mu-Se)(2)(mu-SeCH2Ph)(2)]

The unexpected reaction of triply bonded complexes [(eta (5)-RC5H4)(2)M-2(C O)(4)] with dibenzyl diselenide (PhCH2)(2)Se-2 in toluene at reflux gave a series of isomeric M2Se4 clusters trans/anti-[(eta (5)-RC5H4)(2)M-2(mu -Se) (2)(mu -SeCH2Ph)(2)] (1a, M = Mo, R = MeCO; 2a, Mo, MeO2C; 3a, Mo, EtO2C; 4 a, W, MeCO; 5a, W, MeO2C; 6a, W, EtO2C) and trans/syn-[(eta (5)-RC5H4)(2)M- 2(mu -Se)(2)(mu -SeCH2Ph)(2)] (1b, M = Mo, R = MeCO; 2b, Mo, MeO2C; 3b, Mo, EtO2C; 4b, W, MeCO; 5b, W, MeO2C; 6b, W, EtO2C) in combined 20-41% yields. In addition, the reaction of [(eta (5)-MeO2CC5H4)(2)W-2(CO)(4)] with (PhCH 2)(2)Se-2 in solid state at 90 degreesC also afforded 5a and 5b in a total of 32% yield. The structures of these new clusters were fully characterized by elemental analysis and spectroscopy; those for 3a and 3b were confirmed by single-crystal X-ray diffraction techniques. (C) 2000 Elsevier Science B.V. FLU rights reserved.