.pi. Complexes of nickel(0) and ketones. Mechanism of formation and the crystal structure of (benzophenone)bis(triethylphosphine)nickel

Aldehydes and ketones influence reactivity and selectivity in nickel-catalysed Suzuki–Miyaura reactions

“…19 Ligand exchange, where COD is replaced with the aryl halide, and the oxidative addition event that follows cannot be deconvoluted; we propose that the favourable coordination of aldehydes and ketones to Ni 0 (vide infra) improves the equilibrium position of the ligand exchange (COD versus aryl halide), leading to a reaction that is more rapid overall. Consistent with this, signals that are tentatively assigned to an h 2 (CO) complex are observed during the oxidative addition reactions of 3-Cl; various complexes of this type are known, [23][24][25][26][27][28][29][30] and have been implicated in nickel-mediated reactions. 31 The observed signals in the 31 P{ 1 H} NMR spectrum are consistent with a square planar complex (two doublets with 2 J PP of 31 Hz).…”

The Importance of Ligand‐Induced Backdonation in the Stabilization of Square Planar d10 Nickel π‐Complexes

“…However, this method is generally qualitative, with many examples that fall in the middle of the spectrum being simply described as hybrids of the two resonance forms . Indeed, the C=O bond lengths of the η 2 ‐carbonyl complexes examined here (complexes 1 , 2 , 3 and 6 ) all fall between 131.7–135.4 pm . This range is unfortunately ambiguous because it is in the middle of the typical bond lengths of about 122 and 143 pm for C=O double bonds and C−O single bonds, respectively.…”

“…[71,72] Indeed, the C=Ob ond lengths of the h 2 -carbonyl complexes examinedh ere (complexes 1, 2, 3 and 6)a ll fall between 131.7-135.4 pm. [73][74][75] This range is unfortunately ambiguous because it is in the middle of the typical bond lengths of about 122 and1 43 pm for C=Od ouble bonds and CÀOs ingleb onds, respectively.S imilarly,i nformation about the degree of backbonding can be gleaned from the sum of the bond anglesa boutt he carbon atom of the punit (AE] C ,T able 1). However,t hese results are again inconclusive because the observed AE] C values (= 341-3528)a re intermediate between those expected for planar sp 2 -hybridizeda nd pyramidal sp 3 -hybridized carbon atoms.…”

Benzaldehydebis(tricyclohexylphosphine)nickel(0)

“…The plane of the phenyl group forms an angle of 21.5 (1) ° with plane (I). The structure of the complex benzaldehydebis(tricyclohexylphosphine)nickel(0) resembles the structures of Ni complexes containing ketones like (CF3)2CO (Countryman & Penfold, 1972) and Ph2CO (Tsou, Huffmann & Kochi, 1979). The structure may be described as containing an oxa-nickela-cyclopropane ring.…”