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Capturing a Ghost. Synthesis and Structural Characterization of Pd(dba)[P(o‑Tol)3]2

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posted on 24.06.2013 by Brennen A. Harding, Patrick R. Melvin, William Dougherty, Scott Kassel, Felix E. Goodson
In an effort to improve upon a literature synthesis of bis­[tris­(o-tolyl)­phosphine]­palladium­(0) (1) from tris­(o-tolyl)­phosphine and Pd2(dba)3, we instead isolated a new compound which proved to have the composition Pd­(dba)­[P­(o-Tol)3]2 (2), upon analysis by X-ray crystallography. While this is not the first known palladium compound containing both dba and phosphine ligands, it is, to our knowledge, the first containing dba and tris­(o-tolyl)­phosphine. This is significant, because mixtures of Pd2(dba)3 and tris­(o-tolyl)­phosphine are routinely used in cross-coupling protocols, and palladium complexes containing dba and tris­(o-tolyl)­phosphine have been cited as intermediates in organometallic and polymerization reactions. The most interesting crystallographic parameter for 2 is an abnormally long Pd–P bond length of 2.388(1) Å, which we believe is the cause of this complex’s metastability. We also present an alternative synthesis of 1 that does not require a large excess of phosphine.

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