Arsaalkenes R−AsC(NMe₂)₂ [R = PhC(O), 4-EtC₆H₄C(O), 2,4,6-Me₃C₆H₂C(O), <i>t</i>BuC(O), Me₃Si]: Versatile Reagents in the Chemistry of Heterocumulenes

Reaction of [Cp(CO)2MPC(SiMe3)2] (where M = Mo (3a), W (3b)] with 2 equiv of the arsaalkene PhC(O)AsC(NMe2)2 afforded the metalloarsaalkenes [where M= Mo (6a), W (6b)]. Small amounts of [{η3:η3-(Me3Si)2CPAs−AsPC(SiMe3)2}{Mo(CO)2Cp}2] (7) were formed as a minor product. Similarly, 3b and 2 equiv of 4-EtC6H4C(O)AsC(NMe2)2 gave rise to the formation of (8). However, treatment of 3a and 3b with an excess of tBuC(O)AsC(NMe2)2 yielded cocrystals of the η3-2-phospha-1,3-diarsaallyl complexes [Cp(CO)2M{η3-tBuC(O)AsPAsC(O)tBu}] [where M = Mo (13a), W (13b)] and the η3-1,2,3-triarsaallyl complexes [Cp(CO)2M{η3-tBuC(O)AsAsAsC(O)tBu}] [where M = Mo (14a), W (14b)] in varying ratios. Reaction of 3a with Me3SiAsC(NMe2)2 afforded the dinuclear 1,2-diphosphapropene complex [{η2:η2-(Me3Si)2CP−P(H)−C(H)(SiMe3)2}{Mo(CO)2Cp}2] (15). The novel compounds 6a,b, 8, 13a,b, 14a,b, and 15 were characterized by means of spectroscopy (IR and 1H, 13C{1H}, 31P NMR). Moreover the molecular structures of 7, 8, 13a, 14a, 13b, 14b, and 15 were determined by X-ray diffraction analyses.