Dehydrogenative B−H/C(sp³)−H Benzylic Borylation within the Coordination Sphere of Platinum(II)

Abstract

The first examples of stoichiometric dehydrogenative B-H/C(sp )-H benzylic borylation reactions, which are of relevance to catalytic methylarene (di)borylation, are reported. These unusual transformations involving a (κ -P,N)Pt(η -benzyl) complex, and either pinacolborane or catecholborane, proceed cleanly at room temperature. Density functional calculations suggest that borylation occurs via successive σ-bond metathesis steps, whereby a Pt -H intermediate engages in C(sp )-H bond activation-induced dehydrogenation.

Alkene Isomerization–Hydroboration Catalyzed by First-Row Transition-Metal (Mn, Fe, Co, and Ni) N-Phosphinoamidinate Complexes: Origin of Reactivity and Selectivity

“…Given the likely involvement of nickel hydrido species including (PN)­NiH as key catalytic intermediates, such complexes were of particular interest. Exposure of ((PN)­NiCl) 2 to NaEt 3 BH in THF at room temperature upon workup afforded the dinuclear complex ((PN)­NiH) 2 in 67% isolated yield (Figure ), the connectivity of which was confirmed on the basis of single-crystal X-ray diffraction analysis. The C 2 -symmetric solid-state structure of ((PN)­NiH) 2 is similar to that observed in ((PN)­NiCl) 2 and other Group 10 N -phosphinoamidinate complexes .…”

“…Exposure of ((PN)­NiCl) 2 to NaEt 3 BH in THF at room temperature upon workup afforded the dinuclear complex ((PN)­NiH) 2 in 67% isolated yield (Figure ), the connectivity of which was confirmed on the basis of single-crystal X-ray diffraction analysis. The C 2 -symmetric solid-state structure of ((PN)­NiH) 2 is similar to that observed in ((PN)­NiCl) 2 and other Group 10 N -phosphinoamidinate complexes . Previously reported ((β-diketiminate)­NiH) 2 complexes disclosed by Limberg and co-workers feature tetrahedral coordination about Ni, are paramagnetic, and in solution are prone to loss of dihydrogen either upon thermal activation (25–80 °C, depending on the ancillary ligand substitution) or upon treatment with L-donors such as 4-dimethylaminopyridine (DMAP).…”

“…Whereas we have reported previously on the synthesis of Mn, Fe, and Co (PN)­M variants, preparation of the requisite precatalyst (PN)­Ni has not been described in the literature. Treatment of ((PN)­NiCl) 2 with LiN­(SiMe 3 ) 2 in benzene upon workup afforded (PN)­Ni in near quantitative yield (Figure ). Unlike the analogous paramagnetic Mn, Fe, and Co species, (PN)­Ni is a diamagnetic complex that exhibits sharp 1 H, 13 C­{ 1 H}, and 31 P­{ 1 H} NMR resonances consistent with a C S -symmetric structure (see SI Figures S1–S3).…”

Dehydrogenative B−H/C(sp3)−H Benzylic Borylation within the Coordination Sphere of Platinum(II)

“…[11] Tr eatment of the N-phosphinoamidine 1[H] with (COD)PtCl(benzyl), followed by exposure to base afforded the N-phosphinoamidinate complex 2-Pt in 73 %i solated yield (Scheme 2). The connectivity within 2-Pt was confirmed on the basis of NMR spectroscopic and X-ray crystallographic data ( Figure 1 [12] ). In keeping with the relatively few crystallographically characterized (h 3 -benzyl)platinum complexes reported thus far in the literature, [13] each of the two crystallographically independent molecules of 2-Pt exhibit progressively longer PtÀC distances on going from PtÀCH 2 (2.06-2.07 )t oP t ÀC ipso (2.31-2.32 )t oP t ÀC ortho (2.42-2.44 ); similar trends were observed for the related complexes (k 2 -P,N-1)Pd(h 3 -benzyl) 2-Pd (Pd À C: 2.082(4), 2.233(4), and 2.372(5) )and (k 2 -P,N-1)Ni(h 3 -benzyl) 2-Ni (Ni À C: 1.9584(15), 2.0765(13), and 2.2205 (15) ).…”

Selective, radical-free activation of benzylic C–H bonds in methylarenes

“…1,4 Catalytic activation of benzylic C-H bonds by metal complexes in the absence of radical or basic reagents occurs much less common and often suffers from selectivity issues. [9][10][11][12][13][14][15] The key step for designing general and selective catalytic benzylic C-H functionalisation is selective activation, e. g. oxidative addition of a benzylic C-H bond in a range of unactivated alkylarenes. However, only few complexes mediate oxidative addition of benzylic C-H bonds and, in most cases, is accompanied by oxidative addition of aromatic C-H bonds.…”