Configuration of imino carbon palladated pyridine-2-carbaldimines. Crystal and molecular structure of trans-chlorobis(dimethylphenylphosphine){[(p-methoxyphenyl)-imino](2-pyridyl) methyl}palladium(II)

Article abstract of DOI:10.1021/om00138a012

Reaction of trans-[PdCl(2-C₅H₅N)(L)₂]Cl (2-C₅H₅N = N-protonated 2-pyridyl; L = PMe₂Ph, PEt₃) with an equimolar amount of isocyanide, CNR (R = C₆H₄OMe-p, Me), followed by deprotonation with NEt₃, yields the imino(2-pyridyl)methyl complexes trans-[PdCl{C(2-C₅H₄N)=NR}(L)₂]. These compounds have been characterized by usual spectroscopic techniques and by reaction with ZnCl₂, which gives 1:1 binuclear adducts containing the α-diimino group σ,σ′-N,N′ chelated to the zinc center. ¹H NMR spectra in CD₂Cl₂ indicate a predominant E-trans conformation in the temperature range -80-30°C for the imino carbon palladated organic moiety, when not involved in chelation. This is also the only configuration present in the solid state, as shown by an X-ray crystal structure determination of trans-[PdCl{C(2-C₅H₄N)= NC₆H₄OMe-p}(PMe₂Ph)₂]. This compound crystallizes in the monoclinic system: space group P2₁/n and cell constants a = 16.520 (2) A?, b = 10.953 (1) A?, c = 16.544 (2) A?, β = 97.46 (2)°, and Z = 4. A total of 3969 reflections have been used in the refinement, resulting in a final R value of 0.029. The structure is characterized by a planar N=C-C. .^-N α-diimino skeleton, which is perpendicular to the palladium coordination plane (dihedral angle of 86.4 (2)°) and coplanar with the 2-pyridyl ring (dihedral angle of 1.9 (2)°), whereas the phenyl ring of the C₆H₄OMe-p substituent is rotated by 19.5 (2)°. The coordination around palladium is essentially square-planar, with Pd-C(1) = 2.006 (4), Pd-Cl = 2.430 (2), Pd-P(1) = 2.323 (2), and Pd-P(2) = 2.331 (2) A?.