Asymmetric Synthesis and Metal Complexes of aC₃-Symmetric P-Stereogenic Triphosphine, (R)-MeSi(CH₂PMe(t-Bu))₃(MT-Siliphos)

Abstract

Asymmetric deprotonation of PMe 2 (t-Bu)(BH 3 ) with s-BuLi/ (−)-sparteine, followed by treatment with MeSiCl 3 , gave a 2.6:1 mixture of the C 3 -and C 1 -symmetric triphosphine−boranes MeSi(CH 2 PMe(t-Bu)(BH 3 )) 3 (3). Recrystallization gave highly diastereomerically and enantiomerically enriched C 3 -3. After deprotection with morpholine, the triphosphine (R)-MeSi(CH 2 PMe(t-Bu)) 3 (4; (Me, t-Bu)-Siliphos or MT-Siliphos) was used to prepare the metal complexes [Rh(MT-Siliphos)(norbornadiene)][OTf] (5), Ru(MT-Siliphos)(DMSO)Cl 2 (6), [Ru(MT-Siliphos)(NCMe) 3 ][OTf] 2 (7), M(MT-Siliphos)(PPh 3 ) (M = Pd (8), Pt (9)), Cu(MT-Siliphos)(Cl) (10), and polymeric [Cu 2 Cl 2 (μ-(κ 2 ,κ 1 )-MT-Siliphos)] ∞ (11). The crystal structures of C 3 -3 and of complexes 5, 7, and 11 were determined, and dynamic processes in 6 and 8 were characterized by variable-temperature NMR spectroscopy.

Beyond Triphos – New hinges for a classical chelating ligand

“…A c c e p t e d M a n u s c r i p t Edited April 3 12 Subsequent reports involving R'SiP 3 R derivatives developed the ancillary group [42] and phosphine substituents [43,44]. By substituting the ancillary methyl group in ligand 85 for an ethoxy moiety (86), this allowed the ligand to be anchored to silica via an ether linkage (88) and form tungsten tricarbonyl complexes (87) (Scheme 16).…”

“…Two separate groups adapted the phosphine moieties of the parent ligand 82. Two such derivatives involve the substitution one of the PMe 2 groups for either a PPh 2 (MeSiP 2 Me P Ph , 89) or P i Pr 2 group (MeSiP 2 Me P iPr , 90) [44]; while a separate group achieved asymmetric deprotonation of PMe 2 ( t Bu)(BH 3 ) with s-BuLi/(-)-sparteine, followed by treatment with methyltrichlorosilane to give a mixture of C 3 -and C 1 -symmetric triphosphine-boranes MeSi(CH 2 PMe( t Bu)(BH 3 )) 3 [43]. Repeated recrystallization of these phosphine-borane compounds gave diastereomerically and enantiomerically enriched samples of the C 3 -symmetric ligand, which was subsequently deprotected with morpholine to afford (R)-MeSi(CH 2 PMe( t Bu)) 3 (MeSiP 3 MT , 91).…”

“…The P-stereogenic triphosphine 91 was coordinated to several late transition metals: rhodium (101), ruthenium (102 and 103), palladium (104), platinum (105) and copper (106 and 107) (Scheme 18) [43]. These complexes are mostly unremarkable, forming expected structures with standard bond lengths and angles.…”

“…In acetonitrile this complex exists in equilibrium between a tris-and bis-acetonitrile, mono-triflate complex (103b). The copper complex [CuCl(κ 3 -PhBP 3 MT )] (106) is monomeric in solution, but upon recrystallization underwent phosphine dissociation to form polymeric [Cu 2 Cl 2 (μ-κ 2 ,κ 1 -M a n u s c r i p t Edited April 3 13 PhBP 3 MT )] ∞ (107) [43]. Polymer 107 represents the only well-defined polymer incorporating R'E(CH 2 PR 2 ) 3 ligands.…”

Selective formation of a C3-symmetric P-stereogenic tris(phosphine) via platinum-catalyzed asymmetric alkylation of a tris(secondary phosphine)

“…3 We recently described the asymmetric synthesis of the analogous (Me, t-Bu)-Siliphos (MT-Siliphos) using (-)-sparteine as a stoichiometric chiral auxiliary. 4 To investigate asymmetric catalysis as a potentially more efficient synthetic route, 5 we studied tris(secondary phosphine) 1, 6 whose deprotonation/alkylation was known to give mixtures of C3-and C1-symmetric tris(phosphines). 7 Herein we report the diastereoand enantioselective formation of C3-2 (Triphos*, Scheme 1) via catalytic alkylation of 1 mediated by a chiral platinum complex; repeated recrystallization gave a highly diastereomerically enriched tris(phosphine sulfide) derivative.…”