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] <b>1</b> (DippForm = <i>N</i>,<i>N</i>′-bis­(2,6-diisopropylphenyl)­formamidinate, (CH­(NC₆H₃-^<i>i</i>Pr₂-2,6)₂) with potassium graphite in toluene yielded the dark brown heterobimetallic formamidinatosamarium­(II)/potassium complex [KSm­(DippForm)₃]_<i>n</i> <b>2</b>. Divalent <b>2</b>, a Lewis base solvent free homoleptic species, differs significantly from the related heteroleptic formamidinatosamarium­(II) complex [Sm­(DippForm)₂(thf)₂] <b>3</b> with respect to its constitution, structure, and reactivity toward benzophenone. While <b>2</b> reacts giving complex <b>1</b>, the reaction of <b>3</b> 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) <b>4</b>. The formation of <b>4</b> 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 <b>4Yb</b>. <b>3</b> 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)] <b>5</b> 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)] <b>6</b> as a major product and light yellow unsolvated [Sm­(DippForm)₂{OC­(Ph)₂C₂Ph}] <b>7</b> as a minor product. Molecular structures of complexes (<b>2</b>, <b>4</b>–<b>7</b>) show that κ­(<i>N</i>,<i>N</i>′) bonding between a DippForm and samarium atom exists in all compounds, but in <b>2</b>, DippForm also bridges K and Sm by 1κ­(N):2κ­(N′) bonding and two 2,6-diisopropylphenyl groups are η⁶-bonded to potassium