Heterobimetallic indenyl complexes. Synthesis and structure of cis-[Cr(CO)3(indenyl)RhL2 (L2 = norbornadiene, (CO)2)

Abstract

Reaction of the potassium salt of [(eta6-indenyl)Cr(CO)3] at -30-degrees-C in THF with [Rh(Cl)NBD]2(NBD = norbornadiene) yields cis-[Cr(CO)3(indenyl)] Rh-(NBD), 2. Bubbling CO through a CH2Cl2 solution of 2 produces cis-[Cr(CO)3(indenyl)]Rh(CO)2, 3 in quantitative yield. X-ray analyses show for indenyl-Rh-(NBD), 1: a = 17.506(8) angstrom, b = 11.427(6) angstrom, c = 5.979(4) angstrom, beta = 90.8(2)degrees, space group P2(1)/n. For 2: a = 11.098(6) angstrom, b 17.684(8) angstrom, c = 8.253(5) angstrom, beta = 99.7(2)degrees, space group P2(1)/a. For 3: a = 16.558(8) angstrom, b 12.483(8) angstrom, c = 6.629(4) angstrom, space group P2(1)2(1)2(1). Both 2 and 3 have a doubly-bent indenyl moiety and show strongly distorted coordination modes toward the indenyl ligand of both metals. The driving force leading to such highly distorted structures probably arises mainly from a metal-metal interaction

First Stabilization of 14‐Electron Rhodium(I) Complexes by Hemichelation

“…In anti‐ 2 the Rh I center (formally 18 electrons) was clearly engaged in a dissymmetric η 2 :η 3 coordination mode with the five‐membered ring (Figure 2). Ceccon and co‐workers13b–e demonstrated indeed that, with a similar anion prepared from [(η 6 ‐indene)Cr(CO) 3 ], reactions of [{RhL 2 Cl} 2 ] complexes would lead under thermodynamic control13d to the syn ‐facial η 3 coordination of the Rh center to the five‐membered ring when the L 2 moiety operates limited steric hindrance.…”

“… The sequential reaction of 1 a with n‐ BuLi and [{L 2 RhCl} 2 ] dimers operates different facial selection depending on the steric requirements of L 2 ligands. According to Ceccon et al 13b–e. the η 3 ( syn ‐facial) or η 2 :η 3 ( anti ‐facial) are the preferred coordination modes of the Rh I L 2 moiety to the indenyl ligand with a net thermodynamic drive for the dispersion‐favored syn ‐facial arrangement according to Grimme et al 14.…”

In Silico Acetylene [2+2+2] Cycloadditions Catalyzed by Rh/Cr Indenyl Fragments

“…Inspired by the experimental work by Ceccon et al [33][34][35], we chose the bimetallic catalyst [Cr(CO) 3 IndRhL 2 ], where the second metal group Cr(CO) 3 can be coordinated both in anti and syn conformations and examined both paths I and II of Scheme 3. The optimized molecular structures (ZORA-BLYP/TZ2P) of anti-and syn-[Cr(CO) 3 IndRh(CO) 2 ] ( Figure S1) are in good agreement with the X-ray crystallographic structures (labelled as HEXPOP [50] and HAPPOD [34] in the Cambridge database (CSD) [51]). Significant geometry parameters are compared in Table S1.…”

“…Finally, another modification to a half-sandwich catalyst is the coordination of a second metal to form a bimetallic complex [1] when the aromatic ligand is polycyclic; the second metal can be in syn or anti position. A very nice example, reported by Ceccon et al [33][34][35], is [Cr(CO) 3 IndRh]L 2 (Scheme 2). The idea behind the design of these compounds was that the presence of two metal centers within the same molecule may profoundly affect both the physical properties and the reactivity of the catalyst.…”

“…They found that the Rh/Cr catalyst leads to a greatly enhanced catalytic efficiency compared to the monometallic one. This increase of catalytic activity was ascribed to a synergic or "cooperative" interaction between the two metals in activating the substrate of interest [33][34][35].…”