Homoleptic carbene complexes Part IX.Bis(imidazolin-2-ylidene-1-yl)borate complexes of palladium(II),platinum(II) and gold(I)

摘要

The in situ synthesis of the monoanionic chelating dicarbene ligand bis(imidazolin-2-ylidene-1-yl)borate (BIS~R, R = Me (2a), Et (3a),~i Pr (4a)) from potassium bis(imidazol-l-yl)dihydridoborate (1) via dialkylation with alkyl iodide and deprotonation with Li~Bu is described. Treatment of PdI2 and PtCl2 with THE solutions of BISR (1:2) leads to the first neutral homoleptic tetracarbene complexes of these metals 5—9, which are highly soluble in organic media. According to the X-ray structure analyses of 5. 6 and 9, the bischelates adopt centrosymmetric trans double-boat conformations exhibiting the usual stereochemical features. Neutral heteroleptic dicarbene—phosphine complexes of palladium and platinum of the general formula [M(BLSR)(I)(PEt3)] (14—19) result in good yields from the reaction of BISR with [M4t-CI)Cl(PEt3)], (2:1). From X-ray structure determinations of 15, 16 and 18 two findings should be emphasized: the heavy out-of-plane bending of the boat-shaped chelate ring (which is the cause of chirality of these complexes), and the existence of two rather different M to carbene carbon bond lengths (indicating the stronger trans influence of PEt3 as compared to 1). With Au(CI)(PPh3), instead of forming small chelate rings, the bidentate ligands BISR switch to a ~s2-rj’:~’-bridging ligand type of function giving rise to the compounds 10—12. An X-ray study of 11 reveals the structure of a 12-membered dimetallacycle in a twisted boat-like conformation with a trans-annular Au~- Au separation of 3.3610(7) A, i.e. only a weak interaction. In addition, two by-products-the three-coordinate iodobis(triphenylphos-phine)gold(I) (13) and trans-diiodobis(triethylphosphine)palladium(II) (20)- have been structurally characterized.