Direct Observation of P(O)−C Bond Formation from (N⌒N)PdMe(P(O)(OPh)₂) Complexes. Rate Enhancement of Reductive Elimination by Addition of Triarylphosphines

Complexes of the type (N⌒N)PdMe(P(O)(OPh) 2 ) (N⌒N = bipy ( 1 ), phen ( 2 ), dNbipy ( 3 ); bipy = 2,2‘-bipyridine, phen = 1,10-phenanthroline, Nbipy = 4,4‘-dinonyl-2,2‘-bipyridine) have been synthesized and investigated as intermediates in P(O)−C(sp 3 ) bond-forming reactions. Surprisingly, P(O)−C(sp 3 ) bond formation was not observed upon heating solutions of 1 − 3, even under harsh conditions (toluene- d 8, 110 °C, 48 h). Complexes 1 − 3 are also resistant to reductive elimination in the presence of Lewis bases such as THF, acetonitrile, and P(O)Ph 3 . However, the addition of PPh 3 to solutions of 1 − 3 afforded the alkyl phosphonate MeP(O)(OPh) 2 . This suggests that P(O)−C(sp 3 ) bond formation occurs by reductive elimination from an intermediate of the type (N⌒N)(PPh 3 )PdMe(P(O)(OPh) 2 . The molecular structure determination of 1 is a rare example of a crystallographically characterized transition-metal complex containing a methyl group cis to a phosphonate moiety.