Dirhodium(II) Compounds with Bridging Thienylphosphines: Studies on Reversible P,C/P,S Coordination

Abstract

Monocyclometalated compound [Rh(2){(C(8)H(4)S)P(C(8)H(5)S)(2)}(CH(3)CO(2)H)(2)(O(2)CCH(3))(3)] (1 a) and bis-cyclometalated compound [Rh(2){(C(8)H(4)S)P(C(8)H(5)S)(2)}(2)(CH(3)CO(2)H)(2)(O(2)CCH(3))(2)] (2 a) have been isolated from the reaction of dirhodium tetraacetate and tris(2-benzo[b]thienyl)phosphine (2 BTP) using low acidic solutions. By contrast, in pure acetic acid the reaction of Rh(2)(O(2)CCH(3))(4) with 2 BTP and tris(2-thienyl)phosphine (2 TP), followed by replacement of the axial acetate ligands by chlorides, led to [Rh(2){(2-C(8)H(5)S)P(2-C(8)H(5)S)(2)}(2)Cl(2)(O(2)CCH(3))(2)] (3 b) and [Rh(2){(2-C(4)H(3)S)P(C(4)H(3)S)(2)}(2)Cl(2)(O(2)CCH(3))(2)] (5 b), respectively. These new dirhodium(II) compounds possess equatorial bridging ligands in a phosphorous-sulfur (P,S) coordination mode. The reversible switching between the P,C and P,S bonding mode of the phosphine has been studied in the monocyclometalated [Rh(2){(C(4)H(2)S)P(C(4)H(3)S)(2)}(CH(3)CO(2)H)(2)(O(2)CCH(3))(3)] (6 a), which was selectively transformed into compound [Rh(2){(2-C(4)H(3)S)P(C(4)H(3)S)(2)}(CF(3)SO(3))(CH(3)CO(2)H)(O(2)CCH(3))(3)] (7 c) in triflic acid media. Remarkably, compound 7 c reverts to the starting compound 6 a upon treatment with sodium acetate. Theoretical DFT calculations for both the P,C/P,S rearrangement and the base-promoted reversion have been performed to explain the experimental findings. Data suggest the P,C/P,S rearrangement occurs by means of a "concerted protonation-demetalation mechanism" followed by eta(2) coordination of the thienyl ring and subsequent isomerization to the S-eta(1)-coordination mode. In the reversion reaction, the base coordinated at the axial position would promote a concerted metalation-deprotonation mechanism.

Dirhodium(II)/Xantphos-Catalyzed Relay Carbene Insertion and Allylic Alkylation Process: Reaction Development and Mechanistic Insights

“…The P–Rh distance (2.548 Å) at axial position is longer than that in complex B , which might be caused by the rigid structure. It should be noted that structural chemistry of Rh 2 (O 2 CR) 4‑ x (PC) x ( x = 1 or 2, wherein PC = (C 6 H 5 ) 2 P­(C 6 H 4 )), have been well studied since their first synthesis reported by Cotton et al in 1985. , Complex C can also be obtained in 75% yield from the reaction of Rh 2 (Oct) 4 with Xantphos in toluene at 80 °C for 24 h, and its 31 P NMR spectrum is consistent with the new signals that appear in Figure S9b. The formation of complex C from complex A is probably caused by the release of an octanoate anion and the coordination of the second P atom to Rh to form intermediate III , followed by the subsequent metalation of the phenyl group. , In this vein, a similar dirhodium­(II) complex with a chelating N , N -ligand (2,2′-bipyridine) binding to one of the Rh­(II) atoms and three bridging OAc – groups has been reported in 1991, further supporting that it is reasonable to propose the intermediate III wherein one metal center of the dirhodium core is chelated by the Xantphos ligand.…”

Computational Studies of Carboxylate-Assisted C–H Activation and Functionalization at Group 8–10 Transition Metal Centers

“…calculations (see Figure 42). 176 For the OTf adduct cyclometalation proceeds from an S-bound precursor 102OTf which first rotates to a π-bound intermediate. This then undergoes rate-limiting AMLA/CMD C-H bond cleavage (∆G ‡ ≈ 20 kcal/mol; ∆G ≈ +0.1 kcal/mol) with the marginal endergonicity being consistent with facile H/D exchange.…”

“…Cyclometalation of a tris-(2-thienyl)­phosphine ligand in [(HOAc)­(P­(2-thienyl) 3 )­Rh­(μ-OAc) 3 Rh­(OR′)] ( 102 OR′ , OR′ = OAc, OTf). Adapted with permission from ref . Copyright 2009 John Wiley and Sons.…”

“…Cyclometalation of the tris-(2-thienyl)phosphine ligand in [(HOAc)(P{2-thienyl} 3 )Rh(μ-OAc) 3 Rh(OR′)] dimers (102 OR′ , OR′ = OAc, OTf) has been studied by Lahuerta and Peŕez-Prieto with B3PW91 calculations (see Figure 42). 176 For the OTf adduct, cyclometalation proceeds from an S-bound precursor 102 OTf , which first rotates to a π-bound intermediate. This then undergoes rate-limiting AMLA/CMD C−H bond cleavage (ΔG ⧧ ≈ 20 kcal/mol; ΔG ≈ +0.1 kcal/mol) with the marginal endergonicity being consistent with facile H/D exchange.…”

Molecular Coordination-Switch in a New Role: Controlling Highly Selective Catalytic Hydrogenation with Switchability Function

“…An acid/base-controlled molecular coordination-switch involving two interconvertible metal-coordination modes has been known to chemists for a long time (Figure ). For example, Constable, Wolf, and others demonstrated the reversible switching between the ( Y , S ) and ( Y , C ) coordination modes of thiophene-derived ligands (Y = a pendant pyridine or phosphine ligand or a metal center) with Ru, Os, or Rh metal centers by reaction with acid or base. However, the phenomenon was used merely to achieve a variable spectroscopic, electrochemical, and/or fluorescence excited state property.…”