NMR: A good tool to ascertain σ-silane or σ-borane formulations?

Tert-butylborane: A bis (σ-B–H) ligand in ruthenium hydride chemistry

“…The integrals of the hydrides and the tert-butyl resonances also confirm the presence of one tert-butyl group and four hydrogen atoms around the ruthenium. The 11 B{ 1 H} NMR spectrum exhibits a broad signal at d 69 deshielded (Dd + 10) compared to the resonance of 4, still in a region characteristic of a tricoordinated boron atom [15]. The X-ray structure of 2 was determined at 110 K ( Fig.…”

“…Although the formation of hydrido boryl species in a final B-H bond activation stage has been well documented [12,13] isolated r-borane complexes remain quite rare since the first report in 1996 by Hartwig et al [14]. These complexes often represent key intermediates in the boundary oxidative addition/reductive elimination steps of metal catalyzed reactions [15][16][17][18]. More evidence is now in favour of r-B-H coordinated intermediates as observed in catalyzed borylation processes, thus supporting the recent metathesis mechanism termed r-CAM for late transition metals (r-complex assisted metathesis) and involving metal induced dynamic rearrangements of E-H bonds at constant oxidation state [19].…”

“…Depending first on the nature of the ligands coordinated to the metal fragment and also on the Lewis acidity of the boron atom, dihydroborate coordination resulting from an interaction of the boron with a neighbouring hydride can be favoured [15,[20][21][22]. As part of our ongoing program on B-H bond activation of less-common borane reagents, we started to explore the coordination of monosubstitued boranes RBH 2 .…”

Unsupported boron–carbon σ-coordination to platinum as an isolable snapshot of σ-bond activation

“…A number of σ-alkane complexes have been characterized at low temperature by NMR, but the only structurally characterized examples are topics of debate 8,9 . Isolable σ-complexes range from complexes with weak agostic (that is, supported by a stronger secondary point of ligation) C-H 10,11 , C-C 12,13 and Si-Si 14,15 ligation to strong, unsupported σ-dihydrogen 1,2 and σ-borane complexes [16][17][18][19][20][21][22][23] , whose stability (significantly enhanced in the latter by retrodonation interaction III, Fig. 1a) has led to advances in our understanding of catalytic hydrogenation, hydroboration [24][25][26] , and reversible hydrogen storage by amine-boranes [27][28][29] .…”

Synthesis of a ruthenium bis(diisopropylamino(isocyano)borane) complex from the activation of an amino(cyano)borane

“…[12][13][14] Their syntheses are restricted to salt elimination from organometallic nucleophiles [M(CO) 5 (CN)] − and suitable haloboranes, 12,13 or to isomerization of the BCN linkage of a B-cyanoborane upon coordination to chromium. 12,14,15 As part of our ongoing program on the chemistry of σ-complexes and more particularly on bis(σ-borane) and agostic borane complexes, [16][17][18][19][20] we addressed the synthesis of the amino(cyano)borane i Pr 2 NBH(CN) (2) and its reactivity with the ruthenium precursor [RuH 2 (η 2 -H 2 ) 2 (PCy 3 ) 2 ] (3). We report here the isolation and the characterization of a new cyano ruthenium bis(isocyano)borane complex.…”