Cationic (η⁵-C₅Me₄R)Rh^III Complexes with Metalated Aryl Phosphines Featuring η⁴-Phosphorus plus Pseudo-Allylic Coordination

Abstract

In this contribution we study experimentally and computationally some electrophilic cationic ( 5-C5Me4R)Rh(III) complexes containing a cyclometalated bis(aryl)phosphine, PR'Ar2. The phosphine Ar groups feature methyl substituents at the 2-and 6-positions of the aromatic rings allowing the formation of complexes [( 5-C5Me4R)Rh(C^P)] + (3 +), where the metalated phosphine exhibits  4 coordination to rhodium through phosphorus and the carbon atoms of the adjoining pseudoallylic functionality. The solution and solid-state structure of complexes 3 + has been studied by NMR and X-ray methods, and their electronic properties investigated with the aid of DFT calculations. The Lewis acid behavior of complexes 3 + has also been addressed, concentrating on reactivity toward CO, H2 and hydrosilanes. Some catalytic Si-H/Si-D exchange and hydrosilylation reactions are also reported. With the existing information on the interesting reactivity reported for the parent [( 5-C5Me5)M(Me)(PMe3)(ClCH2Cl)] + (M = Ir, Rh) complexes, 8 particularly in C-H bond activation reactions, the initial objective of this work was to ascertain whether the related metalacyclic complexes [( 5-C5Me5)M(C^P)(ClCH2Cl)] + , incorporating the M-C  bond and the P-donor atom within the chelating C^P ligand, would behave similarly. None of the new compounds prepared was reactive under mild conditions toward intermolecular C-H bond activation, although those derived from the PMeXyl2 ligand, exhibited interesting dynamic and chemical behavior. Instead of the foreseen CH2Cl2 adducts, both the rhodium 4 and the iridium 5a,6 complexes of this ligand featured a metalated phosphine with an unusual  4-coordination involving the phosphorus atom and the contiguous pseudoallylic fragment. This uncommon structural motif is thought to be responsible for their unusual reactivity properties, including intermolecular H-H and Si-H activation, 4 as well as intramolecular C-H oxidative cleavage and CC bond formation. 5a

Thirty Years of (TMS)3SiH: A Milestone in Radical-Based Synthetic Chemistry

“…48 Multiple dehalogenation (41 → 42) is possible in a one-pot procedure by using the corresponding equivalent of reducing agent. 49 Convenient synthesis of deuteriosilane (TMS) 3 SiD by direct H/D exchange mediated either by easily accessible Pt(0) complexes, 50 iridium-pincer complexes, 51 or cationic rhodium complexes 52 have been recently reported. (TMS) 3 SiD is a good reagent for obtaining deuterated products.…”

“…Convenient synthesis of deuteriosilane (TMS) 3 SiD by direct H/D exchange mediated either by easily accessible Pt(0) complexes, iridium-pincer complexes, or cationic rhodium complexes have been recently reported. (TMS) 3 SiD is a good reagent for obtaining deuterated products.…”

β-(Z) Selectivity Control by Cyclometalated Rhodium(III)–Triazolylidene Homogeneous and Heterogeneous Terminal Alkyne Hydrosilylation Catalysts

“…The combination of a supporting Cp* ligand with a strong donor NHC moiety engaged in a five-membered metalacycle, resulting from the ortho metalation of the phenyl substituent, provides a stable structural framework with possible application in hydrofunctionalization reactions. In particular, the Rh–C Ar bond is a reactive site that could participate in the precatalyst activation by reaction with the hydrosilane or the alkyne, thus affording reactive hydrosilylation intermediates . Interestingly, reversible cyclometalation has been proposed as a possible metal–ligand bifunctional mechanism in catalysis .…”

Rhodium‐Catalyzed PIII‐Directed ortho‐C−H Borylation of Arylphosphines

“…In previous rhodium-mediated reactions,w hen the arylphosphine contained an o-tolyl substituent, metalation always occurred preferentially at the benzylic carbon atom, leading to at hermodynamically favored five-membered chelate ring. [21] When dicyclohexyl(o-tolyl)phosphine (9)was coupled with B 2 pin 2 (2a)u nder the standard reactions,C ÀHb orylation only proceeded at the benzylic position (10' ')i no ur system (Scheme 3a). It has been reported that heating of Rh(PPh 3 ) 3 Me in solution gave an orange ortho-metalated four-membered ring complex Ph 2 P(o-C 6 H 4 )Rh with methane.…”