57. "Synthesis, Structure and Spectroscopic Properties of 2,3-bis(diphenylphosphino)quinoxaline (dppQx) and Its Copper(I) Complexes." Cain, M. F.; Reynolds, S. C.; Anderson, B. J.; Glueck, D. S.; Golen, J. A.; Moore, C. E.; Rheingold, A. L. Inorg. Chim. Acta 2011, 369, 55-61.

Abstract

Abstract Phosphinoquinoxalines were prepared by treatment of 2,3-dichloroquinoxaline (3) with phosphorus nucleophiles. The Arbuzov reaction of 3 with PPh(O-i-Pr)₂ gave a mixture of diastereomers of 2,3-(PPh(O)(O-i-Pr))₂quinoxaline (6); the crystal structure of rac-6 was determined, but attempts at reduction to yield bis(phenylphosphino)quinoxaline 7 resulted in P-C cleavage and formation of phenylphosphine.  The bis(secondary phosphine) 7 could be generated from 3 and LiPHPh(BH₃), but was not isolated in pure form.  Copper-catalyzed coupling of PHPh₂ with 3 gave 2,3-bis(diphenylphosphino)quinoxaline (4, dppQx), whose coordination chemistry was investigated, with comparison to data for the analogous 1,2-bis(diphenylphosphino)benzene (dppBz) complexes. Reaction of dppQx with [Cu(NCMe)₄][PF₆] gave [Cu(dppQx)₂][PF₆] (8); CuCl yielded [Cu(dppQx)Cl]₂ (9). Reaction of [Cu(NCMe)₄][PF₆] with one equiv of DPEphos, followed by one equiv of dppQx, gave [Cu(dppQx)(DPEphos)][PF₆] (10).  Ligand 4 and copper complexes 8 and 9 were crystallographically characterized.  The UV-vis spectra of dppQx and its copper complexes were red-shifted from those of the dppBz analogues; in contrast to results for the dppBz complexes, those of dppQx were not luminescent in solution.