Synthesis, Structural Characterization, and Carbonyl Addition Reactivity of a Terminal Cerium(III) Acetylide Complex

Abstract

We report the first structurally characterized terminal Ce(III) acetylide complex, Na[Ce(CCPh)-(bdmmp) 3 ] (2), isolated from the salt metathesis of NaC CPh with Na[Ce(OTf)(bdmmp) 3 ] (1; bdmmp − = 2,6-bis-(dimethylamino)-4-methylphenolate). Compound 2 inserted acetophenone to form the tertiary alkoxide complex Na[Ce-(OC(Me)(Ph)CCPh)(bdmmp) 3 ] (4), rather than forming an enolate product. To the best of our knowledge, complexes 2 and 4 are the first structurally characterized products that exhibit carbonyl group insertion into a Ce−C bond, affording new information on an important class of organocerium reagents.C erium compounds have been used extensively in organic transformations of carbonyl substrates in carbon−hydrogen or carbon−carbon bond forming reactions, including the conversion of ketones to tertiary alcohols. 1,2 Due to their nonbasic nucleophilicity, these cerium-driven reductions occur selectively, even for ketones that readily undergo enolization or pinacol coupling (Scheme 1).

Structural variation in cerium aryloxide complexes templated by hemilabile K+–amine interactions

“…[8][9][10] In a related context, the van Koten group previously reported heterobimetallic rare earth metal complexes of three aryloxides with pendent amino groups in the ortho position, bis(dimethylamino)methyl-4-phenolate (bdmmp): Na[RE(Cl)(bdmmp) 3 ], (RE = Y and Lu). 12 Key here were the liabilities of both the alkali metal and the pendant amine groups, which stabilized the coordination environment at the cerium cation. Recently, we reported a cerium congener with bdmmp À ligands, Na[Ce(OTf)(bdmmp) 3 ] which, upon metathesis with NaCRCPh, produced the first structurally characterized Ce(III)-acetylide complex.…”

Pentamethylcyclopentadienyl‐Supported Cerocene(III) Complexes

“…To our knowledge there is only one reported crystallographically characterized cerium(III) acetylide complex; namely, Na[Ce(C≡CPh)(bdmmp) 3 ] {bdmmp = 2,6‐bis(dimethylamino)‐4‐methylphenolate} . According to the salt metathesis reaction shown in Scheme , employing 1 and lithium tert ‐butylacetylide LiC≡C t Bu, we could obtain ate complexes [Cp* 2 Ce(C≡C t Bu) 2 Li(thf)] ( 4a ) and [{Cp* 2 Ce(C≡C t Bu)} 2 (LiCl)] ( 4b ).…”

“…The Ce–C(acetylide) distance in 4a [2.559(8) Å] is only marginally longer than those in 4b [Ce1–C21 2.549(7) Å; Ce1–C47 2.549(5) Å] and is comparable to the Ce1–C21(benzyl) bond length of 2.573(3) Å in complex 3 . Na[Ce(C≡CPh)(bdmmp) 3 ] features a seven‐coordinate cerium(III) with a considerably longer Ce–C(acetylide) bond of 2.652(9) Å . Interestingly, the C–Ce–C angle in 4a is slightly smaller than in the corresponding yttrium ate complex [Cp* 2 Y(C≡C t Bu) 2 Li(thf)] [81.2(4)° vs. 84.8(6)°].…”

“…By using equimolar amounts of [Cp* 2 Ce{CH(SiMe 3 ) 2 }] and HC≡CR′ (R′ = Me, t Bu) alkane elimination yielded complexes [Cp* 2 Ce(C≡CR)]. Acetylene oligomerization occurred when an excess of the CH‐acidic substrate was used, and the solid‐state structure of [(Cp* 2 Ce) 2 (µ‐η 2 :η 2 ‐RC 4 R)] (R = Me, t Bu) as an intermediate species shed light on the reaction mechanism involved . Notably, complexes Cp* 2 Ln[E(SiMe 3 ) 2 ] (Ln = La, Nd, Sm, Lu; E = N, CH) proved to be excellent precatalysts for ethylene polymerization and hydroamination/cyclization reactions .…”

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2014

“…This was the first structurally characterized product resulting from carbonyl group insertion into a Ce-C bond, affording new information on an important class of organocerium reagents [31]. …”