Preparation and Reactivities of PCP-Type Pincer Complexes of Nickel. Impact of Different Ligand Skeletons and Phosphine Substituents

• Published in: Organometallics Vol. 27; no. 21; pp. 5723 - 5732
• Main Authors: Castonguay, Annie, Beauchamp, André L, Zargarian, Davit
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 10.11.2008; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; PALLADIUM; CATALYSIS; INDENYL COMPLEXES; HYDROSILYLATION; ME; POLYMERIZATION; CRYSTAL; OLIGOMERIZATION; DIPHOSPHINITO POCOP COMPLEXES; NI-II
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om8005454

Reaction of the diphosphine ligand i-Pr2P(CH2)5P(i-Pr)2 with NiBr2 at 110 °C gives a mixture of the 16-membered bimetallacycle {i-Pr2P(CH2)5P(i-Pr)2}2Ni2Br4, 1, and the pincer-type complex {(i-Pr2PCH2CH2)2CH}NiBr, 2; the latter can also be obtained by heating 1 in the presence of 4-(dimethylamino)pyridine or under vacuum. Complex 2 undergoes transmetalation with RMgCl or RLi to give {(i-Pr2PCH2CH2)2CH}NiR (R = Me (4), CCMe (5), Ph (6), n-Bu (7), and CCPh (8)); the phenylacetylide derivative 8 was also obtained from the reaction of PhCCH with 4, 5, or 7. The Ni−Me derivative 4 reacts with PhX (X = I, Br, Cl) to give the product of C−C coupling reaction (Ph−Me) and the Ni−X analogues of 2, and tests have shown that 2 is a competent catalytic precursor for the coupling of PhCl and MeMgCl. The available evidence suggests that this catalytic process does not involve Ni0 intermediates. Indeed, cyclic voltammetry measurements show that 2 can undergo two consecutive oxidations, and attempts to generate isolable high-valent species yielded the five-coordinate, 17-electron NiIII species {(i-Pr2PCH2CH2)2CH}NiX2, 9, from the reaction of 2 with FeX3 (X = Cl, Br). Characterization of all new complexes, including X-ray diffraction studies on single crystals of complexes 1−6 and 9, is described.