Issue 2, 2021

P-Alkynyl functionalized benzazaphospholes as transmetalating agents

Abstract

Exposure of 10π-electron benzazaphosphole 1 to HCl, followed by nucleophilic substitution with the Grignard reagent BrMgCCPh afforded alkynyl functionalized 3 featuring an exocyclic –C[triple bond, length as m-dash]C–Ph group with an elongated P–C bond (1.7932(19) Å). Stoichiometric experiments revealed that treatment of trans-Pd(PEt3)2(Ar)(I) (Ar = p-Me (C) or p-F (D)) with 3 generated trans-Pd(PEt3)2(Ar)(CCPh) (Ar = p-Me (E) or p-F (F)), 5, which is the result of ligand exchange between P–I byproduct 4 and C/D, and the reductively eliminated product (Ar–C[triple bond, length as m-dash]C–Ph). Cyclic voltammetry studies showed and independent investigations confirmed 4 is also susceptible to redox processes including bimetallic oxidative addition to Pd(0) to give Pd(I) dimer 6-Pd2-(P(t-Bu)3)2 and reduction to diphosphine 7. During catalysis, we hypothesized that this unwanted reactivity could be circumvented by employing a source of fluoride as an additive. This was demonstrated by conducting a Sonogashira-type reaction between 1-iodotoluene and 3 in the presence of 10 mol% Na2PdCl4, 20 mol% P(t-Bu)Cy2, and 5 equiv. of tetramethylammonium fluoride (TMAF), resulting in turnover and the isolation of Ph–C[triple bond, length as m-dash]C–(o-Tol) as the major product.

Graphical abstract: P-Alkynyl functionalized benzazaphospholes as transmetalating agents

Supplementary files

Article information

Article type
Paper
Submitted
14 apr 2020
Accepted
16 dec 2020
First published
17 dec 2020

Dalton Trans., 2021,50, 599-611

Author version available

P-Alkynyl functionalized benzazaphospholes as transmetalating agents

D. Y. Zhou, P. M. Miura-Akagi, S. M. McCarty, C. H. Guiles, T. J. O'Donnell, W. Y. Yoshida, C. E. Krause, A. L. Rheingold, R. P. Hughes and M. F. Cain, Dalton Trans., 2021, 50, 599 DOI: 10.1039/D0DT01367F

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