Cobalt(II) and iron(II) tris(trimethylsilyl)siloxides: synthesis, structure and reactivity

Abstract A series of cobalt(II) and iron(II) siloxide complexes, [(Me 3 Si) 3 SiO] 2 M(L n ) {M=Co, L n =none ( 1 ), (THF) ( 3 ), (THF) 2 ( 4 ), (DME) ( 5 ), (MeCN) 2 ( 6 ), (PhCN) 2 ( 7 ), (2,2′-dipyridyl) ( 8 ), 4,4′-dipyridyl ( 9 ), (Ph 3 P) 2 ( 10 ); M=Fe, L n =none ( 2 ), (2,2′-dipyridyl) ( 11 ) were prepared by the reaction of metal silylamides [(Me 3 Si) 2 N] 2 M (M=Co, Fe) with tris(trimethylsilyl)silanol. The crystal structures of compounds 1 and 11 have been determined by the X-ray diffraction method. Complex 1 has a dimeric structure with two [(Me 3 Si) 3 SiO] 2 Co units bonded via the two μ 2 -O atoms. The central [Co(μ 2 -O)] 2 cycle has a ‘butterfly shape’ being bent along the bridging oxygen atoms. The dihedral angle between the Co(1)O(4)Co(2) and Co(1)O(3)Co(2) planes is 143.1°. The μ 2 -bridging and terminal CoO distances are 1.945(7)–1.963(7) and 1.781(8), 1.793(7) A, respectively. The Co⋯Co distance in 1 is relatively short, 2.735(2) A. However, the high value of magnetic moment (6.0 μ B ) of compound 1 indicates the absence of a direct interaction between the Co atoms in 1 . The molecule of 11 is monomeric. The Fe atom is bonded to 2,2′-dipyridyl and two terminal OSi(SiMe 3 ) 3 groups and has a distorted tetrahedral environment. The FeN(1), FeN(2) and FeO(1), FeO(2) distances in 11 are 2.148(1), 2.164(1) and 1.863(1), 1.900(1) A, respectively. Addition of one equivalent of PhCCH to 7 results in the substitution of one tris(trimethylsilyl)siloxy-group with the formation of the diamagnetic dimer {(PhCN)(PhC 2 )CoOSi(SiMe 3 ) 3 } 2 . Subsequent addition of PhC 2 H causes its oligomerisation. Complexes 1 , 3 and 10 absorb carbon monoxide at ambient temperature and pressure while the others remain unreactive. Electronic spectra show fluxional behavior of complexes 1 , 3 and 4 in solution.