Palladium(II) Pincer Complexes Derived From N,N’,N’’‐Tris(2‐thioanisyl)guanidine. Syntheses, Structural Aspects, Solution Behaviour and Suzuki‐Miyaura Coupling Reactions

Abstract

Guanidine, [(ArNH)2C=NAr] (Ar=2‐(MeS)C6H4) was prepared in 70 % (method 1)/92 % (method 2) yields. Cyclopalladation of the guanidine with Pd(OC(O)R)2 (R=Me and tBu) afforded the CNS pincer complexes, [Pd{κ3(C,N,S)}(OC(O)R)] in 82 % and 75 % yields, respectively. [Pd{κ3(C,N,S)}(OC(O)R)] (R=Me and tBu) upon metathesis reaction with LiBr gave [Pd{κ3(C,N,S)}Br] in 67 % and 72 % yields, respectively. The reaction of [Pd{κ3(C,N,S)}Br] with AgBF4 in MeCN gave [Pd{κ3(C,N,S)}(MeCN)]BF4 in 82 % yield. The new compounds were characterised by elemental analysis, IR and NMR spectroscopies and mass spectrometry. Molecular structures of [(ArNH)2C=NAr] (Ar=2‐(MeS)C6H4) and [Pd{κ3(C,N,S)}(OC(O)tBu)] were determined by single crystal X‐ray diffraction while the solution behaviour of the former compound studied by VT 1H NMR spectroscopy. [Pd{κ3(C,N,S)}(OAc)] was used as a catalyst in Suzuki‐Miyaura coupling reactions of aryl bromides with aryl boronic acids.

Guanidine-centred reactivity of CNN Pd(ii) pincer complexes including carboxylate-assisted N–H activation and –CH2– → –C(O)– oxygenation

“…These structural differences between the two sets of guanidines mentioned above were anticipated to influence the course of their reactions with Pd(OC(O)R 0 ) 2 . Continuing our interest in CNE Pd(II) pincer complexes (E = N and S), 14,15 herein, we report the reactions of guanidines 1 and 2 with Pd(OC(O)R 0 ) 2 with the objective of identifying the substituent effects of the starting materials upon the types of complexes formed. In this endeavour, we were able to isolate four distinct pincer complexes A (3-8), B (10-14), C (17) and D (15 and 16) as illustrated in Scheme 1 and these complexes were fully characterised.…”