Reactivity
of Bulky Formamidinatosamarium(II or III)
Complexes with CO and CS Bonds
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Abstract
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 CS<sub>2</sub> are discussed. Treatment of the tris(formamidinato)samarium(III)
complex [Sm(DippForm)<sub>3</sub>] <b>1</b> (DippForm = <i>N</i>,<i>N</i>′-bis(2,6-diisopropylphenyl)formamidinate,
(CH(NC<sub>6</sub>H<sub>3</sub>-<sup><i>i</i></sup>Pr<sub>2</sub>-2,6)<sub>2</sub>) with potassium graphite in toluene yielded
the dark brown heterobimetallic formamidinatosamarium(II)/potassium
complex [KSm(DippForm)<sub>3</sub>]<sub><i>n</i></sub> <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)<sub>2</sub>(thf)<sub>2</sub>] <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)<sub>2</sub>(thf){μ-OC(Ph)(C<sub>6</sub>H<sub>5</sub>)C(Ph)<sub>2</sub>O}Sm(DippForm)<sub>2</sub>]
(C<sub>6</sub>H<sub>5</sub> = 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 OCPh<sub>2</sub> fragment. An analogous reaction
of [Yb(DippForm)<sub>2</sub>(thf)<sub>2</sub>] gives an isostructural
complex <b>4Yb</b>. <b>3</b> reacts with carbon disulfide
forming a light green dinuclear formamidinatosamarium(III) complex
[{Sm(DippForm)<sub>2</sub>(thf)}<sub>2</sub>(μ-η<sup>2</sup>(C,S):κ(S′,S″)-SCSCS<sub>2</sub>)] <b>5</b> through an unusual C–S coupling induced by an amidinatolanthanoid
species giving the thioformylcarbonotrithioate ligand. The trivalent
organometallic [Sm(DippForm)<sub>2</sub>(CCPh)(thf)] complex activates
the CO bond of benzophenone by an insertion reaction, forming
the light yellow [Sm(DippForm)<sub>2</sub>{OC(Ph)<sub>2</sub>C<sub>2</sub>Ph}(thf)] <b>6</b> as a major product and light yellow
unsolvated [Sm(DippForm)<sub>2</sub>{OC(Ph)<sub>2</sub>C<sub>2</sub>Ph}] <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 η<sup>6</sup>-bonded to potassium
