N-Triisopropylphenyl-substituted N,Npy,O pincers as supports for mononuclear palladium(II) complexes and hydrogen-bonded dimeric assemblies

Treatment of the sterically bulky 2-(3-biphenyl-2-ol)-6-iminepyridine, 2-(3-C12H8-2-OH)-6-(CHN(2,4,6-i-Pr3C6H2))C5H3N (HL1tripp), with Pd(OAc)2 or (MeCN)2PdCl2 results in deprotonation of HL1tripp to afford the discrete square planar O,Npy,N-pincer complexes, [(L1tripp)Pd(OAc)] (1) and [(L1tripp)PdCl] (2) respectively, in good yield; conversion of 1 directly to 2 using aqueous sodium chloride or to [(L1tripp)PdI] (3) using aqueous sodium iodide has been demonstrated. Selective reduction of the imino unit in HL1tripp with LiAlH4 proceeds smoothly to yield the 2-(3-biphenyl-2-ol)-6-methylaminepyridine, 2-(3-C12H8-2-OH)-6-(CH2-NH(2,4,6-i-Pr3C6H2))C5H3N (HL2tripp), which on reaction with Pd(OAc)2 at low temperature gives [(L2tripp)Pd(OAc)] (4) as the sole product. Complex 4 exists as a dimeric species in the solid state in which two square planar monomers are linked together by two intermolecular NHamine⋯Oacetate interactions resulting in a Pd⋯Pd separation of 6.255 Å. The corresponding chloride complex, [(L2tripp)PdCl] (5), formed by reaction of 4 with aqueous sodium chloride, also exists as a dimeric assembly in the solid state but in this case the presence of two intermolecular NHamine⋯Ophenolate interactions has the effect of compressing the palladium–palladium separation to 3.2580(11) Å. Single crystal X-ray diffraction studies have been performed on 1, 2·CH2Cl2, 2·C6H6, 3, 4 and 5.

Graphical abstractThe secondary amine unit within a tripp-substituted Namine,Npy,O pincer, has been employed as a hydrogen bond donor to direct the self-assembly of dimeric palladium(II) complexes with metal⋯metal separations between 6.225 and 3.2580(11) Å; conversely with the corresponding imine-based pincer, discrete monomeric square planar palladium species are accessible.Figure optionsDownload full-size imageDownload as PowerPoint slide