Beyond Dehydrocoupling: Group 2 Mediated Boron–Nitrogen Desilacoupling

Liptrot, David J.; Arrowsmith, Merle; Colebatch, Annie L.; Hadlington, Terrance J.; Hill, Michael S.; Kociok‐Köhn, Gabriele; Mahon, Mary F.

doi:10.1002/anie.201507004

Cited by 33 publications

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“…We have recently reported that reaction of the silylborane pinBSiMe 2 Ph with the β-diketiminato magnesium n -butyl derivative [HC{(Me)CN(Dipp)} 2 Mg n- Bu] (7) provides ready access to the magnesium silyl species [HC{(Me)CN(Dipp)} 2 MgSiMe 2 Ph] ( 8 ) through elimination of a n- BuBpin by-product46. This reaction was envisaged to ensue via a four-membered σ-bond metathesis transition state, the assembly of which was facilitated by the relative polarity of the Mg–C and Si–B bonds and the ability of boron to increase its coordination number in a β-position to the magnesium centre.…”

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confidence: 99%

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

et al. 2017

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Organoboranes are some of the most synthetically valuable and widely used intermediates in organic and pharmaceutical chemistry. Their synthesis, however, is limited by the behaviour of common boron starting materials as archetypal Lewis acids such that common routes to organoboranes rely on the reactivity of boron as an electrophile. While the realization of convenient sources of nucleophilic boryl anions would open up a wealth of opportunity for the development of new routes to organoboranes, the synthesis of current candidates is generally limited by a need for highly reducing reaction conditions. Here, we report a simple synthesis of a magnesium boryl through the heterolytic activation of the B–B bond of bis(pinacolato)diboron, which is achieved by treatment of an easily generated magnesium diboranate complex with 4-dimethylaminopyridine. The magnesium boryl is shown to act as an unambiguous nucleophile through its reactions with iodomethane, benzophenone and N,N′-di-isopropyl carbodiimide and by density functional theory.

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confidence: 99%

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

et al. 2017

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“…[18][19][20] TheM g À Si interaction of 2.6022(9) is slightly longer than that reported for 1 of 2.5900 (7) . [18] Due to difficulty in isolation, anumber of these species were isolated as solvates containing coordinating ethers. 2a·THF and 4a·OEt 2 exhibit longer MgÀSi bonds (2.614(1) and 2.664(3) respectively) than 1,consistent with the higher coordination number at Mg.…”

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“…A number of lithium and magnesium silyls were synthesized . Magnesium silyl reagents ( 1 – 4 ) were prepared by a two‐step procedure involving sequential deprotonation of the pro‐ligand (β‐diketiminate, iminoanilide or guanidine) with [Mg n/s Bu 2 ] followed by a metathesis reaction with R 3 Si‐Bpin (Figure ) . In an alternative approach, lithium silyls ( 5⋅THF , 5⋅TMEDA, 5⋅PMDETA ) were synthesised by direct metalation of PhMe 2 SiCl with Li metal (Figure ).…”

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confidence: 99%

“…[8,9] Magnesium silyl reagents (1-4)w ere prepared by at wo-step procedure involving sequential deprotonation of the pro-ligand (b-diketiminate,i minoanilide or guanidine) with [Mg n/s Bu 2 ]f ollowed by am etathesis reaction with R 3 Si-Bpin ( Figure 1). [18] In an alternative approach, lithium silyls (5·THF, 5·TMEDA, 5·PMDETA)w ere synthesised by direct metalation of PhMe 2 SiCl with Li metal (Figure 1). 5·THF was isolated as adark-red oil and based on 1 HNMR spectroscopic analysis contains 1.5 THF molecules per silicon atom.…”

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Defluorosilylation of Industrially Relevant Fluoroolefins Using Nucleophilic Silicon Reagents

et al. 2019

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An umber of new magnesium and lithium silyl reagents were prepared and shown to be outstanding nucleophiles in reactions with industrially relevant fluoroolefins. These reactions result in an et transformation of either sp 2 or sp 3 CÀFbonds into CÀSi bonds by two modes of nucleophilic attack( S N VorS N 2'). The methods are mild, proceeding with high chemo-and regioselectivity.M echanistic pathways are described that lead to new substitution patterns from HFO-1234yf,H FO-1234ze,a nd HFO-1336mzz, previously inaccessible by transition metal catalyzeddifluorosilylation routes.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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“…[8] We reasoned that this apparently limited onward reactivity was al ikely consequence of the sterically demanding ORTEP representation (25 %thermal ellipsoids) of 2 with hydrogen atoms removed for clarity. [9] Selected bond lengths [] and angles [8 8]: Mg-N2 2.0128(13), Mg-N1 2.0173(13),M g-Si 2.5900 (7), N2-Mg-N19 3.40 (5), N2-Mg-Si 130.76 (4), N1-Mg-Si 135.81 (4).…”

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Beyond Dehydrocoupling: Group 2 Mediated Boron–Nitrogen Desilacoupling

et al. 2015

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The alkaline-earth element bis(trimethylsilyl)amides,[ Ae{N(SiMe 3 ) 2 } 2 (thf) 2 ][ Ae = Mg, Ca, Sr],a re effective precatalysts for boron-nitrogen bond formation through the desilacoupling of amines,RR'NH (R = alkyl, aryl;R' = H, alkyl, aryl), and pinBSiMe 2 Ph. This reactivity also yields as toichiometric quantity of Me 2 PhSiH and provides the first example of ac atalytic main-group element-element coupling that is not dependent on the concurrent elimination of H 2 .The selective catalytic formation of element-element bonds is of vital importance for the synthesis of both molecular and macromolecular entities.W hile am ajority of attention will remain fixated on the construction of C À Ca nd C À E( E= pblock element) bonds,t here is growing interest in the development of catalytic routes to homonuclear EÀE( E= B, Si, Sn, P, As,etc.) and heteronuclear EÀE' (e.g.E= B, E' = N; E= Si, E' = N, O) linkages. [1] Without exception, all of these latter advances have been achieved through the catalytic dehydrocoupling of E À Ha nd E À Ho rE À Ha nd E' À Hsubstrates with concomitant elimination of dihydrogen (Scheme 1). While such dehydrogenative methods will undoubtedly continue at the forefront of p-block cross-coupling,t his chemistry is critically dependent on the availability of suitable E À Hand E' À Hsubstrates. Forthe heavier p-block elements in particular, this latter requirement is likely to impose as evere limitation on the ultimate scope of available reactivity.I ti sc lear, therefore,t hat the construction of increasingly sophisticated p-block molecules and materials will be greatly facilitated by the development of alternative and more generalized protocols for the catalytic assembly of EÀE and EÀE' bonded species.Theu se of catalytic reagents derived from the heavier alkaline-earth elements (Ae = Mg, Ca, Sr, and Ba) is attractive on account of their high terrestrial abundance and low toxicity. [2] In the case of these elements,a ccess to catalytic manifolds through E/E' À Ho xidative addition steps commonly associated with many transition-metal-based catalyses is precluded by the stability of the 2 + oxidation state.Rather, successive small-molecule activation steps must be effected through s-bond metathesis and related reaction processes,the efficacyo fw hich is dictated by both the polarization and relative basicity of the substrates and catalytic intermediates. Acase in point is provided by the group 2catalyzed Si À H/H À Nh eterodehydrocoupling of hydrosilanes and amines, HNR 1 R 2 (R 1 ,R 2 = H, alkyl, aryl;S cheme 2). [3] Theo rientation of each dihydrogen-and silazane-producing metathesis transition state shown as A and B in Scheme 2i sdictated by the relative polarization of the hydridic SiÀHand acidic NÀH functions and the polarization of the substituent bonding to the highly electropositive alkaline-earth center.T wo recent reports serve to highlight af urther subtlety.K inetic and computational analysis of reactions utilizing tris(oxazolinyl)borato magnesium or anilidoimine barium reagents has...

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Beyond Dehydrocoupling: Group 2 Mediated Boron–Nitrogen Desilacoupling

Cited by 33 publications

References 30 publications

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

Defluorosilylation of Industrially Relevant Fluoroolefins Using Nucleophilic Silicon Reagents

Beyond Dehydrocoupling: Group 2 Mediated Boron–Nitrogen Desilacoupling

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