Crystal and molecular structure of 4-[(diethylamino)(t-butylamino)methylene]-4-(t-butyl isocyanide)-2,2,5,5-tetrakis(trifluoromethyl)-1,3,4-dioxapalladolan: a palladium(II) carbene complex

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Abstract
Crystals of the title compound (I) are monoclinic, space group P21/a, with Z= 4 in a unit cell of dimensions: a= 20·093(3), b= 9·519(2), c= 15·201(3)Å, β= 96·77(2)°. The structure has been elucidated by conventional heavy-atom methods from 4123 diffracted intensities measured on a four-circle diffractometer, and refined to R 0·099. The palladium atom, which is in an approximately square-planar environment, forms part of a five-membered condensed hexafluoroacetone ring, [graphic omitted], which is of envelope conformation. The O–C(CF3)2 bond from the oxygen atom adjacent to the metal in this ring is notably short [1·337(13)Å]. The plane of the carbene ligand lies perpendicular to the co-ordination plane of the Pd atom; there is virtually no back-donation from Pd to carbene [Pd–C(4) 2·07 Å], and the carbene lies trans to C(1) of the five-membered ring. The C–N bond distances within the carbenoid fragment (mean 1·32 Å) indicate a high degree of delocalisation. The short intramolecular contact between the H atom of the NHBut group and one of the methylene hydrogen atoms of the NEt2 group supports spectroscopic evidence for restricted rotation around an N–Et bond.

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