Well-Defined BisMETAMORPhos Pd^I–Pd^I Complex: Synthesis, Structural Characterization, and Reactivity

Abstract

The formation of a bisMETAMORPhos PNbridged dimeric Pd I complex (3) from ligand 1 and Pd(dba) 2 is described. The addition of 1 to Pd(dba) 2 initially leads to the formation of Pd 0 complex 2, which has a highly distorted tetrahedral environment and binds two neutral ligands 1. Complex 2 converts to {Pd I } 2 complex 3 upon heating. Complex 3 consists of a completely flat Pd−Pd core, with a Pd−Pd bond length of 2.6199(4) Å, and the Pd centers display a highly distorted square planar coordination environment. The formation of complex 3 from 2 is suggested to proceed via an in situ comproportionation pathway. Initial decoordination of one ligand from 2 followed by oxidative addition of one neutral coordinated ligand arm leads to a 1-Pd II H complex. Insertion of free dba into the Pd−H bond generates a 1-Pd II dba complex that releases 1,5-diphenylpent-1-en-3-one via intra-or intermolecular protonolysis. Concomitantly, comproportionation with 1-Pd 0 yields 3. Complex 3 was found to function as a precatalyst in the Suzuki−Miyaura cross-coupling of p-chloroacetophenone with good conversions.

Dinuclear Palladium Complexes with Two Ligand‐Centered Radicals and a Single Bridging Ligand: Subtle Tuning of Magnetic Properties

“…This result confirms that the chloridobridged dinuclearc omplex, although stable, does not persist in the presence of ab etter ligand.I ta lso suggestst hat it might be possible to exchange bridgehead groups in case an on-neutral co-ligand is employed. When as olution of complex 1 in CH 2 Cl 2 is treated with an equimolar amount of TlPF 6 in the presence of PPh 3 ,c omplex 3 is formed as the only product with full conversion of 1.N otably, 31 PNMR spectroscopy on paramagnetic 3 reveals the coordinated phosphine as as harp singlet at d = 28.63 ppm (the chemical shift is indicative of coordination to Pd) [23] and the PF 6 anion as af ully resolved septet, while the 1 HNMR spectrum displays four broad resonances between d = 8.36 and 1.19 ppm. Although it appears that dinuclear 2 is susceptible to reaction with additional ligand and potentially also metalloligand species, we reasoned that access to otherm onoatom-bridged dinuclearp alladium diradical species could be more easily achieved by using am ixture of chloride species 1 and an eutral, non-chloride-containing analogue, [Pd(X)(NNO ISQ )].T he in situgenerated cationic [Pd(NNO ISQ )] speciess hould then be trapped selectively by this non-chloridod erivativet of orm an ew monoatom-bridged dinuclear diradical.…”

Facile Synthesis and Versatile Reactivity of an Unusual Cyclometalated Rhodium(I) Pincer Complex

“…[13] However,w ea re unaware of any strategies to exploit both hemilabile agostic interactions and reversible cyclometalationa sp art of ar eactive ligand concept in coordination chemistry. [14][15][16] Understanding of and control over the reactivity of the metal-carbon fragment might ultimately enablet he use of this bond type in cooperative catalysis.…”

“…ORTEP (ellipsoids setat5 0% probability) for complex 4 (front and side view). Selectedb ond lengths []and angles[8]: Rh1-P12 .2259(3), Rh1-N1 2.0594(11), Rh1-C1 2.3750(15),Rh1···H112 .192(19), Rh1-C21 1.8363(15); P1-Rh1-N1 82.92(3),P 1-Rh1-C11160.08(4), P1-Rh1-C21 94.99(4), N1-Rh1-C11 77.25(4);t orsion aN1-C5-C6-C11 À31.87(16).Chem. Eur.J.2015, 21,7297 -7305 www.chemeurj.org as ingle well-defined species (Scheme 5).…”

Designing Pd and Ni Catalysts for Cross-Coupling Reactions by Minimizing Off-Cycle Species

“…Further, these two factors also promote the productive off-cycle activation of the catalyst, which involves the formal reduction of the Pd(II) precatalyst to the Pd(0) active species. The in-situ generation of the Pd(0) highly reactive species can also promote further off-cycle chemistry, including the formation of dimers, 45,46,47,48 trimers, 49,50 nanoparticles 51 or Pd-black, 52 which can be detrimental to catalysis. However, when properly formulated, polynuclear complexes can also be highly efficient cross-coupling precatalysts.…”