m-Terphenyl Anchored Palladium Diphosphinite PCP-Pincer Complexes That Promote the Suzuki−Miyaura Reaction Under Mild Conditions

Abstract

Diphosphinite PCP-pincer pro-ligands anchored by a meta-terphenyl backbone were synthesized. These pro-ligands, [2,6-(2-Ph2POC6H4)2C6H3X] (3a X = I, 3b X = Br) and [2,6-(2- i Pr2POC6H4)2C6H3X] (4a X = I, 4b X = Br) upon reaction with Pd2(dba)3 yield PCP palladium pincer complexes [2,6-(2-Ph2POC6H4)2C6H3PdX] (5a X = I, 5b X = Br) and [2,6-(2- i Pr2POC6H4)2C6H3PdX] (6a X = I, 6b X = Br). The structures of 5a−b and 6a−b were determined by single crystal X-ray diffraction analyses. Complexes 5b and 6b were evaluated for their efficacy in promoting catalytic Suzuki−Miyaura CC coupling reactions. A variety of aryl bromides efficiently underwent CC coupling reactions with p-tolylboronic acid with high yields in the presence of either 5b or 6b. Compound 6b also proved to be a very active pro-catalyst for the coupling of aryl chlorides with p-tolylboronic acid. Excellent to good yields (in some cases greater than 90%) were achieved even with electron rich or sterically hindered aryl chlorides.

Improved synthesis of pincer ligand precursor, and synthesis and structural characterization of terphenyl scaffolded S–C–S palladium pincer complex

“…Compound 2 had proved versatile in the formation of N-C-N and P-C-P pincer ligand precursors [6][7][8][9], and as expected, did so for an S-C-S analogue. Thus reaction of 2 and Li[S(p-Tol)] (freshly prepared by reaction of the thiol with nBuLi) readily yields compound 3 as a yellow oil in 87% yield (Scheme 3) [14].…”

“…Another attribute displayed is the great adaptability and variability of the ligand platform. Our recent efforts [6][7][8][9] have centered on a particular extension of one common pincer ligand motif, the meta-xylyl backbone (A, Chart 1). The introduction of additional aryl rings between the anchoring phenyl ring and the donor atoms forces the resulting pincer complexes (B, Chart 1) to be considerably non-planar owing to larger chelate ring sizes.…”

Novel access to carbodiphosphoranes in the coordination sphere of group 10 metals: template synthesis and protonation of PCP pincer carbodiphosphorane complexes of C(dppm)2

“…13 C { 1 H} NMR (CD 2 Cl 2 /MeOH): δ 21.8 ( 1 J(P2C) = 93.6, 2+3 J(P1C) = 5.0, C1), 40.9 ( 1 J(P1C) = 19.4, 1 J(P2C) = 71.1, 3 J(P3C) = 5.0, C2), 129.9 ( 1 J(P1C) = 47.3, 3 J(P2C) = 5.5, Ph1-C ipso ), 133.6 ( 2 J(P1C) = 14.6, Ph1-C ortho ), 129.2 ( 3 J(P1C) = 12.5, Ph1-C meta ), 132.9 (Ph1-C para ), 126.9 ( 1 J(P2C) = 85.0, 3 J (P1C) = 7.5, Ph2-C ipso ), 132.6 ( 2 J(P2C) = 10.4, Ph2-C ortho ), 129.1 ( 3 J(P2C) = 11.5, Ph2-C meta ), 131.7 (Ph2-C para ). 1 H NMR (CD 2 Cl 2 ): δ 3.95 ( 2 J(P1H) = 9.5, 2 J(P2H) = 7.1, CH 2 ), 7.10-7.80 (m,.…”

Facile synthesis of achiral and chiral PCN pincer palladium(II) complexes and their application in the Suzuki and copper-free Sonogashira cross-coupling reactions

“…While the reaction of more reactive 4-bromoacetophenone with PhB(OH) 2 in the presence of 0.1 mol% of Uozumi's PCP-bis(phosphinite) pincer Pd complex at 110°C only gave a 60% yield after 24 h [23]. Very recently, Protasiewicz reported that similar m-terphenyl anchored symmetrical PCP-bis(phosphinite) pincer Pd complexes could promote the CC coupling of aryl bromides with p-tolylboronic acid at 50°C and the catalysis was thought to occur via a Pd(0)-Pd(II) catalytic cycle [40]. However, the coupled products were obtained in only moderate yields with 1 mol% of catalyst after 20 h in the case of bromobenzene and 2-bromotoluene (76% and 45%, respectively).…”