Reactivity of [Pd{CH2C(O)Me}Cl] n toward Isocyanides

• Published in: Organometallics 2005-05, Vol.24 (10), p.2516-2527
• Main Authors: Vicente, José, Arcas, Aurelia, Fernández-Hernández, Jesús M, Bautista, Delia, Jones, Peter G
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om048999c

[Pd{CH2C(O)Me}Cl] n (1) reacts at low temperature with RNC (RNC:Pd = 1 or 2) to give [Pd2{CH2C(O)Me}2(μ-Cl)2(CNR)2] [R = tBu (2a), Xy (2b)] or trans-[Pd{CH2C(O)Me}Cl(CNR)2] [R = tBu (5a), Xy (5b)], respectively. These complexes decompose at room or higher temperature to give [Pd2{κ2-C,O-C(NHR)CHC(O)Me}2(μ-Cl)2] [R = tBu (3a), Xy (3b)] or [Pd{κ2-C,O-C(NHR)CHC(O)Me}Cl(CNR)] [R = tBu (6a), Xy (6b)], respectively, via insertion of the isocyanide into the Pd−C bond plus a tautomerization process from β-ketoimine to β-ketoenamine. The complex [Pd{κ2-C,O-C(NHXy)CHC(O)Me}Cl(NCMe)] (4b) can be obtained by reacting 1 with XyNC (Pd:XyNC = 1) in MeCN or complex 3b in CHCl3 with excess MeCN. Complexes trans-[Pd{C(NHR)CHC(O)Me}Cl(CNR)2] [R = tBu (8a), Xy (8b)] can be obtained (i) by reacting 1 with RNC (RNC:Pd = 3) or better (ii) by reacting 6 with 1 equiv of RNC at low temperature. The Pd(I) complexes [Pd2Cl2(CNR)4] [R = tBu (7a), Xy (7b)] are decomposition products obtained by heating 1 with RNC (RNC:Pd = 4−5), but they are detected in trace amounts in the reaction of 1 with RNC (RNC:Pd = 2−3). Addition of RNC and KTfO to a cooled suspension of 1 (Pd:RNC:KTfO = 1:3:1) gives complexes [Pd{CH2C(O)Me}(CNR)3]TfO [R = tBu (9a), Xy (9b)], which decompose at room temperature. The decomposition of 9b gives [Pd{κ2-C,O-C(NHXy)CHC(O)Me}(CNXy)2]TfO (10b), which can be obtained, as can the corresponding 10a, by reacting complexes 6 with 1 equiv of TlTfO and RNC. The reactions of the dimers 3 with PPh3 (Pd:PPh3 = 1) gives [Pd{κ2-C,O-C(NHR)CHC(O)Me}Cl(PPh3)] [R = tBu (11a), Xy (11b)], with PEt3 (PEt3:Pd = 2), trans-[Pd{C(NHR)CHC(O)Me}Cl(PEt3)2] [R = tBu (12a), Xy (12b)], and with Tl(acac) (Pd:acac = 1), [Pd{κ2-C,O-C(NHR)CHC(O)Me}(κ-O,O-acac)] [R = tBu (13a), Xy (13b)]. The crystal structures of 6a, 9b, 10a, and 10b have been determined. In complex 10b there are intermolecular π−π stacking and C−H···Pd agostic interactions giving dimers.