Alkyne-coordinating tridentate ligands: structural properties and reactivity of their rhodium complexes

Abstract

Complexes of novel alkyne-chelating tridentate ligands bound to a rhodium atom were isolated and characterised. The present alkyne-rhodium complex underwent dimerisation simply by heating to afford the unprecedented cyclobutadiene dirhodium complex. It is also found that the ligands at the trans positions influence the π-coordination of alkynes.

Pyridine‐Enhanced Head‐to‐Tail Dimerization of Terminal Alkynes by a Rhodium–N‐Heterocyclic‐Carbene Catalyst

“…The 1 H NMR spectrum of 3 displayed the typical signals for coordinated pyridine, in addition to a broad signal at d = 3.52 ppm (CH) and two doublets at d = 2.45 and 2.04 ppm (CH 2 ), which correspond to the h 2 -alkyne. [37] The 13 C{ 1 H}-APT NMR experiment at low temperature corroborates the assigned structure for 3. The carbene carbon atom signal appeared as a doublet at d = 182.8 ppm with a J CÀRh value of The formation of 3 is in accordance with a plausible first step consisting of coordination of the triple bond to the metallic center (see below).…”

Chemistry of N,S‐Heterocyclic Carbene and Metallaboratrane Complexes: A New η3‐BCC‐Borataallyl Complex

“…The C11À C12 bond length of 1.389(7) i sc onsistentw ith ad ouble bond, similart ot hose observed in other rhodium p-alkene complexes (Table 1). [27][28][29][30][31][32] Along with the CÀCd istances,v arious structuralp arameters and 13 CNMR chemical shifts of as eries of Rh-alkene complexes are listed in Table 1, which corroborate well with those of compound 4.T he C13ÀO2 distance (1.342 (6) ) is slightly shorter than as ingle bond length, which may be due to the participation in resonance of the ester group.…”

Bimetallic Reactivities of Dinuclear Iridium and Rhodium Complexes Generated from Two Types of Alkyne‐Containing Bisphosphine Ligands

“…However, their reactivities remain unclear because of robustness of structures toward ligand exchange. During the course of our investigations on P – alkyne – P tridentate ligands, we found the formation of butadiene‐1,4‐diyl diiridium(II,II) complex 3 (1 st generation) bearing an iridium–iridium bond by complexation of ligand 1 with an iridium(I) precursor (Scheme b). [8b] Complex 3 has an extraordinary stability against moisture and air despite its carbon–iridium bonds, which is probably due to chelation of four phosphine ligands.…”

“…During the course of our investigations on P – alkyne – P tridentate ligands, we found the formation of butadiene‐1,4‐diyl diiridium(II,II) complex 3 (1 st generation) bearing an iridium–iridium bond by complexation of ligand 1 with an iridium(I) precursor (Scheme b). [8b] Complex 3 has an extraordinary stability against moisture and air despite its carbon–iridium bonds, which is probably due to chelation of four phosphine ligands. Moreover, complex 3 has an iridium–iridium bond so that it can effectively incorporate several monatomic cations between two iridium centers without significant structural change.…”