Exploiting the Versatility of Phosphinobenzylsilanes for the Stabilization of 14‐Electron Rhodium(III) and Iridium(III) Complexes

Abstract

Incorporating pendant silicon functionalities into phosphine ligands enables to profit from the strong σ‐electron donor and trans influence properties of Si while enhancing the coordination ability of the ligand. Herein, we show that the introduction of bulky sigma donor substituents on the Si atoms and modulation of the number of Si–H functional groups in a series of phosphinobenzylsilanes allow either the stabilization of rare highly unsaturated 14‐electron rhodium(III) and iridium(III) species devoid of agostic interactions or the access to mixed‐valence MI–MIII complexes. Our findings using isopropyl‐substituted silicon are markedly different from those obtained when employing the methyl‐substituted Si series.

Different Reactivities of (5-Ph2P-Ace-6-)2MeSiH toward the Rhodium(I) Chlorides [(C2H4)2RhCl]2 and [(CO)2RhCl]2. Hirshfeld Atom Refinement of a Rh–H···Si Interaction

“…All of these values are similar to or are within the standard uncertainty reported for the related [Cy 2 P­( o -C 6 H 4 )] 2 SiMe-Rh­(H)Cl (Rh–H 1.51(3) Å; Rh–Si 2.2616(7) Å; Si–H 2.14(3) Å; Si–Rh–H 65.8(12)°) . Furthermore, the Rh–Si bond reported for 1 is slightly longer than the Rh­(III)–Si distances of the silyl hydrides ( i Pr NNN)­Rh­(H)­SiHRPh (2.2301(8) Å, R = Ph; 2.2466(7) Å, R = H) and the phosphinodisilane [RhCl­{κ 3 ( P , Si , Si )-PhP­( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 }] (2.293(2) Å) . The Rh­(I) complex 2 consists of a longer Rh–Si bond (2.3887(5) [2.3759(5)] Å), which is still in the range for a covalent bond ( vide infra ) …”

“…Furthermore, 2D 29 Si– 1 H HMBC NMR revealed a 1 J (Si–H Rh ) coupling constant of 5 Hz, which is slightly larger than in [Cy 2 P­( o -C 6 H 4 )] 2 SiMe-Rh­(H)Cl (3 Hz). The 1 J (Rh–P) coupling constants of 112 Hz ( 1 ) compare well to the reported 1 J (Rh–P) coupling constants of [Cy 2 P­( o -C 6 H 4 )] 2 SiMe-Rh­(H)Cl (118 Hz), and RhHX 1 X 2 {xant­(P i Pr 2 ) 2 } (99–114 Hz) and the phosphinodisilane [RhH­{κ 3 ( P , Si , Si )-PhP­( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 }] (111 Hz), whereas the 1 J (Rh–P) value of 2 (140/142 Hz) is larger as expected for Rh­(I) species versus Rh­(III). , The 1 J (Rh–Si) values of 23 Hz ( 1 ) and 16 Hz ( 2 ) are similar but are smaller than the J couplings reported for the phosphinodisilane [RhH­{κ 3 ( P , Si , Si )-PhP­( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 }] (39 Hz) and for the silyl hydrides ( i Pr NNN)­Rh­(H)­SiHRPh (31.2 Hz, R = Ph; 33.2 Hz; R = H) . No 1 J (Rh–Si) value has been reported for [Cy 2 P­( o -C 6 H 4 )] 2 SiMe-Rh­(H)­Cl.…”

“…in rhodium­(III) silyl hydrides of the type ( i Pr NNN)­Rh­(H)­SiHRPh ( i Pr NNN = 2,5-[ i Pr 2 P = N­(4- i PrC 6 H 4 )] 2 N­(C 6 H 2 ) − ) reported at 26 Hz (R = H) and 26 Hz (R = Ph) . They are also marginally larger than in the phosphinodisilane [RhH­{κ 3 ( P , Si , Si )-PhP­( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 }] with 1 J (Rh–H) = 25 Hz or in Xantphos rhodium­(III) species of the type RhHX 1 X 2 {xant­(P i Pr 2 ) 2 } (X 1 , X 2 = H, Cl, OTf; xant = 9,9-Me 2 -4,5-( i Pr 2 P) 2 -C 12 H 6 O) binding one or two hydrides, giving rise to J couplings of 24–26 Hz . Within the latter study, the reported RhH 2 OTf­{xant­(P i Pr 2 )} shows a larger 1 J (Rh–H) coupling of 31 Hz in comparison to our reported complex 1 .…”

“…100 Furthermore, the Rh−Si bond reported for 1 is slightly longer than the Rh(III)−Si distances of the silyl hydrides ( iPr NNN)-Rh(H)SiHRPh (2.2301(8) Å, R = Ph; 2.2466(7) Å, R = H) 101 and the phosphinodisilane [RhCl{κ 3 (P,Si,Si)-PhP(o-C 6 H 4 CH 2 Si i Pr 2 ) 2 }] (2.293(2) Å). 102 The Rh(I) complex 2 consists of a longer Rh−Si bond (2.3887(5) [2.3759(5)] Å), which is still in the range for a covalent bond (vide infra). 107 The results discussed for 1 are based on Hirshfeld atom refinement (HAR), and we present the first comparison of a standard HAR 86 for a transition-metal hydride to a novel NoSpherA2 HAR.…”

Functionalized NU-1000 with an Iridium Organometallic Fragment: SO2 Capture Enhancement

“…As part of our research program aimed at developing organometallic complexes for catalytic and environmental applications, we have synthesized a series of modularly variable semiflexible pincer-like ligand architectures, silylphosphine ligands, with varying electronic and steric properties. , We have proved that the tridentate ligand [PhP­( o -C 6 H 4 CH 2 Si i Pr 2 H) 2 ] is able to stabilize coordinatively unsaturated 14-electron Ir­(III) centers, namely, [XIr­{κ 3 (P,Si,Si)­PhP­( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 }] (X = halogen, Me, CH 2 SiMe 3 , etc .). We proposed that the incorporation of some of these complexes into MOF material NU-1000 would enhance the catalytic activity and the gas adsorption properties of the MOF due to the availability of additional coordination sites at the Ir metal to host SO 2 in either η 1 or η 2 coordination modes, the electronic stabilization of Ir by the strong sigma donor ligand, and even the possibility to free an additional coordination site.…”