Carbene vs Olefin Products of C−H Activation on Ruthenium via Competing α- and β-H Elimination

Abstract

Bulky pincer complexes of ruthenium are capable of C-H activation and H-elimination from the pincer ligand backbone to produce mixtures of olefin and carbene products. To characterize the products and determine the mechanisms of the C-H cleavage, reactions of [RuCl(2)(p-cymene)](2) with N,N'-bis(di-tert-butylphosphino)-1,3-diaminopropane (L1) and 1,3-bis(di-tert-butylphosphinomethyl)cyclohexane (L2) were studied using a combination of X-ray crystallography, NMR spectroscopy, and DFT computational techniques. The reaction of L1 afforded a mixture of an alkylidene, a Fischer carbene, and two olefin isomers of the 16-e monohydride RuHCl[(t)Bu(2)PNHC(3)H(4)NHPBu(t)(2)] (2), whereas the reaction of L2 gave two olefin and two alkylidene isomers of 16-e RuHCl[2,6-(CH(2)PBu(t)(2))(2)C(6)H(8)] (3), all resulting from dehydrogenations of the ligand backbone of L1 and L2. The key intermediates implicated in the C-H activation reactions were identified as 14-electron paramagnetic species RuCl(PCP), where PCP = cyclometalated L1 or L2. Thus the alpha- and beta-H elimination reactions of RuCl(PCP) involved spin change and were formally spin-forbidden. Hydrogenation of 2 and 3 afforded 16-electron dihydrides RuH(2)Cl(PCP) distinguished by a large quantum exchange coupling between the hydrides.

Phosphino‐amine (PN) Ligands for Rapid Catalyst Discovery in Ruthenium‐Catalyzed Hydrogen‐Borrowing Alkylation of Anilines: A Proof of Principle

“…The X-ray structure of this 18-e species reveals a trans-Cl-Ru-H center supported by a dehydrogenated 3b unit, which now acts as a three-coordinate mer ligand through the two P atoms and the η 2 -olefin moiety. A similar structure has already been reported by Gusev et al [27] The coordination sphere in 7 is completed by a P(OMe)Ph2 group, likely from the P-N bond methanolysis [28] of a second 3b molecule. The hydridic resonance in 7 is found at -13.58 ppm (apparent td), and the olefinic signals appear at δ 5.38 (dd, 3 JHP = 13.6, The isolated 3b/Ru(II) complexes 4 and 7 were tested in the model benzylation reaction of aniline.…”

A Square‐Planar Ruthenium(II) Complex with a Low‐Spin Configuration

“…[5] However, according to density functional theory (DFT) calculations, the PCP pincer complex [RuCl{HC(CH 2 NHPtBu 2 ) 2 }] (A) was postulated to be an unstable intermediate with square-planar coordination geometry and a triplet ground state (IS). [6] Therefore, the related PNP pincer complexes [RuX{N(SiMe 2 CH 2 PtBu 2 ) 2 }] (X = F (B F ), Cl (B Cl ), OTf (B OTf )) remain the only square-planar ruthenium(II) compounds that are experimentally accessible and have an IS ground-state configuration. [7] DFT calculations showed that the highest singly occupied molecular orbital (SOMO) of B Cl exhibits strong d xz -orbital character owing to the p interaction with the disilylamido p donor (Scheme 1, middle).…”

“…However, this interaction is not sufficient to effect spin pairing. Accordingly, square-planar d 6 14-electron complexes with an electronic low-spin configuration are not known, to date. [8,9] Starting from the chelating amino ligand HN(CH 2 CH 2 PiPr 2 ) 2 (HPNP iPr ), we recently reported the synthesis of octahedral ruthenium(II) amino complexes and the corresponding five-coordinate amides.…”

Ein quadratisch‐planarer Ruthenium(II)‐Komplex mit Low‐Spin‐ Konfiguration

“…Geburtstag gewidmet Die Koordinationschemie von d 6 -Ionen der Gruppe 8 wird dominiert von oktaedrischen Komplexen. Vierfachkoordination tritt vor allem bei tetraedrischen Eisenkomplexen auf, die im High-Spin-Zustand (S = 2, HS) vorliegen.…”