Reactivity of Bulky Formamidinatosamarium(II or III) Complexes with CO and CS Bonds

The preparation of a new heterobimetallic
samarium­(II)
formamidinate complex and selected reactions of samarium­(II) complexes
and one samarium­(III) formamidinate complex with benzophenone or CS2 are discussed. Treatment of the tris­(formamidinato)­samarium­(III)
complex [Sm­(DippForm)3] 1 (DippForm = N,N′-bis­(2,6-diisopropylphenyl)­formamidinate,
(CH­(NC6H3-iPr2-2,6)2) with potassium graphite in toluene yielded
the dark brown heterobimetallic formamidinatosamarium­(II)/potassium
complex [KSm­(DippForm)3]n 2. Divalent 2, a Lewis base solvent free homoleptic
species, differs significantly from the related heteroleptic formamidinatosamarium­(II)
complex [Sm­(DippForm)2(thf)2] 3 with respect to its constitution, structure, and reactivity toward
benzophenone. While 2 reacts giving complex 1, the reaction of 3 with benzophenone generates the
highly unusual [Sm­(DippForm)2(thf)­{μ-OC­(Ph)(C6H5)­C­(Ph)2O}­Sm­(DippForm)2]
(C6H5 = 1,4-cyclohexadiene-3-yl-6-ylidene) 4. The formation of 4 highlights a rare C–C
coupling between a carbonyl carbon and the carbon at the para position
of a phenyl group of the OCPh2 fragment. An analogous reaction
of [Yb­(DippForm)2(thf)2] gives an isostructural
complex 4Yb. 3 reacts with carbon disulfide
forming a light green dinuclear formamidinatosamarium­(III) complex
[{Sm­(DippForm)2(thf)}2(μ-η2(C,S):κ­(S′,S″)-SCSCS2)] 5 through an unusual C–S coupling induced by an amidinatolanthanoid
species giving the thioformylcarbonotrithioate ligand. The trivalent
organometallic [Sm­(DippForm)2(CCPh)­(thf)] complex activates
the CO bond of benzophenone by an insertion reaction, forming
the light yellow [Sm­(DippForm)2{OC­(Ph)2C2Ph}­(thf)] 6 as a major product and light yellow
unsolvated [Sm­(DippForm)2{OC­(Ph)2C2Ph}] 7 as a minor product. Molecular structures of complexes
(2, 4–7) show that κ­(N,N′) bonding between a DippForm
and samarium atom exists in all compounds, but in 2,
DippForm also bridges K and Sm by 1κ­(N):2κ­(N′)
bonding and two 2,6-diisopropylphenyl groups are η6-bonded to potassium.