Electron‐Rich, Bicyclic Biaryl‐Like KITPHOS Monophosphines via [4+2] Cycloaddition between 1‐Alkynylphosphine Oxides and Anthracene: Highly Efficient Ligands for Palladium‐Catalysed CN and CC Bond Formation

Abstract

Electron-rich, bicyclic biaryl-like KIT-PHOS monophosphines have been prepared via Diels-Alder cycloaddition between 1-alkynylphosphine oxides and anthracene in an operationally straightforward and highly modular synthetic protocol that will allow access to an architecturally and electronically diverse family of ligands. Palladium complexes of these ligands are highly efficient catalysts for the Buchwald-Hartwig amination and Suzuki-Miyaura coupling of a wide range of aryl chlorides, which for the vast majority of substrate combinations outperform their o-(dicyclohexylphosphino)biphenyl-based counterparts.

Gold(I) Complexes of KITPHOS Monophosphines: Efficient Cycloisomerisation Catalysts

“…[8] The similarity be- tween KITPHOS and Buchwalds biaryl monophosphines, combined with the fact that the latter have proven to be very successful ligands for a vast array of gold-catalysed transformations [9] prompted us to synthesise gold complexes of these KITPHOS monophosphines and investigate their applications in a selection of gold-catalysed cycloisomerisations.…”

Gold‐Catalyzed Cyclizations: A Comparative Study of ortho,ortho′‐Substituted KITPHOS Monophosphines with their Biaryl Monophosphine Counterpart SPHOS

“…[14] As we have previously prepared and crystallographically characterized gold(I) complexes of a number of unsubstituted and monosubstituted KITPHOS monophosphines, single-crystal X-ray analyses of 12a, 12b and 14 were undertaken to compare their key structural features; [15] perspective views of the molecular structures are shown in Figure 4. In each case the gold atom clearly adopts a near linear geometry with P(1) À Au(1) À N(1) angles of 177.19 (9)8 (12a), 177.63(15)8 (12b) and 174.76(9)8 (14) while the Au À P(1) bond lengths of 2.2208(9) (12a), 2.2380(16) (12b) and 2.2374 (8) (14) are all similar and comparable to those reported for gold(I) complexes of electron-rich biarylmonophosphines [16] and KITPHOS monophosphines. [10a,11] Figure 4 also reveals that the proximal aryl ring is orientated parallel and close to the Au À P bond such that there is a weak h 1 -interaction between the gold atom and the ipso carbon atom of the aryl ring; the Au···C ipso distances of 3.187 (12a), 3.176(7) (12b) and 3.133 (7) (14) are less than the sum of the van der Waals radii and similar to the Au···C ipso interactions reported for gold(I) complexes of PCy 2 (o-biphenyl) [16c] and 11-(dicyclohexylphosphino)-12-(2-methoxyphenyl)-9,10-dihydro-9,10-ethenoanthracene.…”

“…1,7-Octadiyne, rac-BINAP and 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (SPHOS) were purchased from commercial suppliers and used without further purification. 11-(Dicyclohexylphosphinoyl)-12-(2,6-dimethylphenyl)-9,10-dihydro-9,10-etheno-A C H T U N G T R E N N U N G anthracene (8a), [11] 11-(dicyclohexylphosphinoyl)-12-(2,6-di-A C H T U N G T R E N N U N G methoxyphenyl)-9,10-dihydro-9,10-ethenoanthracene (8b), [11] 2-(dicyclohexylphosphinoylethynyl)anisole (9), [8] [RhCl(cycloocta-1,5-diene)] 2 , [22] (tht)AuCl, [23] and substrates 15, 17, 19, 21 and 23 were prepared as previously described. H} NMR spectra were recorded on JEOL LAMBDA-500, ECS-400 or Bruker Avance 500 instruments.…”

“…To this end we have recently developed the biaryl-like KITPHOS class of monophosphine 8, [8] which is architecturally similar to Buchwald's biaryl monophosphines in that the PR 2 group is connected to a double bond, albeit not an aryl ring but an anthracene-derived bicyclic framework, and there is a proximal non-phosphine containing aryl ring which can be systematically modified since it is derived from a 1-alkynylphosphine oxide. Encouragingly, our early studies showed that electron-rich KTPHOS monophosphines were highly efficient ligands for palladium-catalyzed C À C and C À N bond formation [8] and that ortho,ortho'-substitution of the proximal aryl ring enhances catalyst performance compared with the corresponding systems based on their unsubstituted or monosubstituted counterparts. [9] Moreover, electron-rich KITPHOS monophosphines either competed with or outperformed their biaryl-based counterparts in palladiumcatalyzed cross-coupling which prompted us to extend our studies to include gold-catalyzed cyclizations.…”

“…[3] Buchwald's biarylmonophosphines such as 1 and 2 provided the lead ligand for this area and since their introduction a number of alternative highly efficient systems such as pyrrole-and indolyl-based monophosphines 3, 4 and 5, respectively, [4,5] BippyPhos 6, [6] and Figure 1. Biaryl monophosphines (1 and 2), pyrrole-based (3) and indolyl-based (4 and 5) phosphines and BippyPhos (6), BI-DIME (7) and KITPHOS (8).…”