Synthesis, structure, and reactivity of doubly trans-spanning bis(dialkyl selenide) complexes; a new route to diselenamacrocycles via alkene metathesis in metal coordination spheres

Abstract The reaction of selenium with NaBH 4 and Br(CH 2 ) 6 CH=CH 2 (2.0 equiv each) gives the dialkyl selenide Se((CH 2 ) 6 CH=CH 2 ) 2 (91% after workup) which is combined with PtCl 2 (0.5 equiv, toluene) to give trans -PtCl 2 (Se((CH 2 ) 6 CH=CH 2 ) 2 ) 2 ( 10 , 85%). The reaction of 10 and Grubbs' first generation catalyst yields macrocyclic ( 11 , 60%) as a mixture of syn / anti isomers with respect to the selenium lone pairs. The reaction of 11 and Ph 2 Zn gives the diphenyl complex ( 12 , 86%; mixture of isomers). When 11 is treated with H 2 under conditions that hydrogenate related diphosphine complexes (5 bar, 50 °C, (Ph 3 P) 3 RhCl or PtO 2 , CH 2 Cl 2 ), no reaction occurs. Under more forcing conditions, (8 bar, 85 °C, Pd/C, C 2 H 5 OH), 11 and 12 give the demetalated diselenamacrocycle Se(C 14 H 28 ) 2 Se ( 13 ; 72-67%). The crystal structures of 11 and 12 show anti selenium lone pairs and trans C=C linkages; that of 13 exhibits columns of extended macrocycles.