Tetramethylphosphinane as a new secondary phosphine synthon

Abstract

Secondary phosphines are important building blocks in organic chemistry as their reactive P—H bond enables construction of more elaborate molecules. In particular, they can be used to construct tertiary phosphines that have widespread applications as organocatalysts, and as ligands in metal-complex catalysis. We report here a practical synthesis of the bulky secondary phosphine synthon 2,2,6,6-tetramethylphosphinane (TMPhos). Its nitrogen analogue tetramethylpiperidine, known for over a century, is used as a base in organic chemistry. We obtained TMPhos on a multigram scale from an inexpensive air-stable precursor, ammonium hypophosphite. TMPhos is also a close structural relative of di-tert-butylphosphine, a key component of many important catalysts. Herein we also describe the synthesis of key derivatives of TMPhos, with potential applications ranging from CO2 conversion to cross-coupling and beyond. The availability of a new core phosphine building block opens up a diverse array of opportunities in catalysis.

Hydrogen Activation with Ru-PN3P Pincer Complexes for the Conversion of C1 Feedstocks

“…An alternative bulky phosphine 2,2,6,6-tetramethylphosphinane (TMPhos), recently developed by some of us, 35 was also investigated as it provides a similar but subtly different stereoelectronic environment compared to P t Bu 2 groups. The new ligand PN 3 P-TMPhos was obtained in 47% yield from 2,6-diaminopyridine and chloro-TMPhos (1-chloro-2,2,6,6-tetramethylphosphinane).…”

“…Pincer ligands of the types PCNCP and PN 3 P such as those shown in Scheme and similar PNN systems, as well as the related MACHO ligand types, − have featured prominently in this area as they can be reversibly protonated and deprotonated. − This has made these ligands particularly attractive for hydrogenations using H 2 activation reactions via metal–ligand cooperative (MLC) behavior, − although recent discoveries suggests that this MLC behavior may not be essential for all catalyst systems . Here, we present our studies on the synthesis of a series of ruthenium(II) complexes featuring PN 3 P-R ligands (where R = t Bu and TMPhos) and their reactivity toward H 2 and CO, as well as their application in the hydrogenation of CO and CO 2 .…”

“… 25 − 30 This has made these ligands particularly attractive for hydrogenations using H 2 activation reactions via metal–ligand cooperative (MLC) behavior, 31 − 34 although recent discoveries suggests that this MLC behavior may not be essential for all catalyst systems. 23 Here, we present our studies on the synthesis of a series of ruthenium(II) complexes featuring PN 3 P-R ligands (where R = t Bu and TMPhos 35 ) and their reactivity toward H 2 and CO, as well as their application in the hydrogenation of CO and CO 2 .…”

Dioxaphosphabicyclooctanes: small caged phosphines from tris(hydroxymethyl)phosphine

“…We have been interested in developing new routes to bulky diphosphine ligands for sustainable catalytic applications. 1,2 However, common precursors, PCl 3 and PH 3 , are extremely hazardous to use and difficult to store. PCl 3 is highly corrosive, whereas PH 3 is pyrophoric and acutely toxic (its short term exposure limit is <1 mg m −3 , even lower than that for HCN!).…”