Insertion of CO and SO 2 into the N–N bond of [Fe 2(CO) 6( μ-Ph 2N 2)

Abstract

The N–N bond of the azobenzene ligand in [Fe 2(CO) 6( μ-Ph 2N 2)] ( 1) is unusually labile. In addition to being cleaved by incorporation of CO or H 2, it also inserts CO resulting from phosphine substitution at the iron atoms. Complexes [Fe 2(CO) 5(PR 3)( μ-PhN–CO–NPh)] ( 2a,b) and [Fe 2(CO) 4{P(OMe) 3} 2( μ-PhN–CO–NPh)] ( 2c) are formed with PPh 3 and P(OMe) 3. Bis(diphenylphosphino)methane produces [Fe 2(CO) 4( η 1-dppm) 2( μ-PhN–CO–NPh)] ( 2d). All these complexes also result from [Fe 2(CO) 6( μ-PhN–CO–NPh)] ( 2) and the corresponding phosphine. Reaction of 1 with SO 2 yields the insertion product [Fe 2(CO) 6( μ-PhN–SO 2–NPh)] ( 4). Complex 4 does not react with CO at temperatures up to its decomposition point. Its thermal degradation in the absence of CO, however, produces the CO insertion product 2, which involves SO 2 elimination with intermediate re-formation of 1. Treatment of 4 with phosphines results only in CO displacement, producing [Fe 2(CO) 5P(OMe) 3( μ-PhN–SO 2–NPh)] ( 4b), [Fe 2(CO) 4(PR 3) 2( μ-PhN–SO 2–NPh)] ( 4a,c, PR 3=PPh 3 or P(OMe) 3), and [Fe 2(CO) 4( μ-dppm)( μ-PhN–SO 2–NPh)] ( 4d). For comparison with the basic structures of 1, 2 and 4 two CO insertion products and two SO 2 insertion products were characterized by crystal structure determinations.