Functionalization of Carbon Monoxide and tert‐Butyl Nitrile by Intramolecular Proton Transfer in a Bis(Phosphido) Thorium Complex

Abstract

We report intramolecular proton transfer reactions to functionalize carbon monoxide and tert-butyl nitrile from ab is(phosphido) thorium complex. The reaction of (C 5 Me 5 ) 2 Th[PH(Mes)] 2 ,M es = 2,4,6-Me 3 C 6 H 2 ,w ith 1atm of CO yields (C 5 Me 5 ) 2 Th(k 2 -(O,O)-OCH 2 PMes-C(O)PMes),i n which one CO molecule is inserted into each thoriumphosphorus bond. Concomitant transfer of two protons, formerly coordinated to phosphorus,a re nowb ound to one of the carbon atoms from one of the inserted CO molecules. DFT calculations were employed to determine the lowest energy pathway. With tert-butyl nitrile, t BuCN,only one nitrile inserts into at horium-phosphorus bond, but the proton is transferred to nitrogen with one phosphido remaining unperturbed affording (C 5 Me 5 ) 2 Th[PH(Mes)][k 2 -(P,N)-N(H)C-(CMe 3 )P(Mes)].S urprisingly,r eaction of this compound with KN(SiMe 3 ) 2 removes the proton bound to nitrogen, not phosphorus.Carbon monoxide is aC 1 feedstock molecule with relatively inert chemistry owing to the strength of the CO bond. [1] The transformation of non-renewable products,s uch as CO and CO 2 ,i nto starting materials and value-added chemicals is desirable.T his has been accomplished for decades using Fischer-Tropsch chemistry in which CO and H 2 are converted into liquid hydrocarbons. [2] However,t his reaction requires acatalyst as well as elevated temperature and pressure.Thus, novel techniques for hydrogen addition to CO,i ncluding stoichiometric reactions,w ould enhance our knowledge of functionalizing CO into hydrocarbons.Mid-to late-transition metal carbonyl complexes are well known. In contrast, the actinides are large,h ighly electropositive metals with minimal metal-ligand bonding interaction, and their valence orbitals have little need for p-acceptor ligands.T herefore,C Oi sapoor ligand for felements,w ith few examples. [3][4][5][6][7][8][9] However,t hese characteristics make actinides well-suited for small molecule activation of oxygenated substrates. [10,11] While reductive coupling of CO is readily accomplished by low-valent f-element complexes such as U III , [12][13][14][15][16][17][18][19][20] Sm II , [21] and aL a III dinitrogen complex, [22] the most common reaction with CO is migratory insertion and CÀC bond formation. [23][24][25][26][27][28][29][30][31][32] However,t wo reports describe the reductive coupling of CO with U III complexes,a nd have observed proton migration to carbon, but only upon heating. [33,34] Our group has been exploring the unusual reactivity of actinide-phosphorus bonds to exploit hard-soft differences, [35] as well as the weak actinide-phosphorus bond which should be effective for small molecule activation. Thei nsertion of CO into at horium-, scandium, or hafnium-phosphorus bond has been previously reported. [36][37][38][39] Both of these reactions produce h 2 -acyl products.H erein, we report the reactivity of the bis(phosphido) complex, (C 5 Me 5 ) 2 Th[PH(Mes)] 2 , [40] Mes = 2,4,6-Me 3 C 6 H 2 ,w ith CO in which both protons are transferred from ph...

An Alkali-Metal Halide-Bridged Actinide Phosphinidiide Complex

“…The distance of Th−N is 2.262(4) Å, whereas the distance of Th−P is 2.771(1) Å. Moreover, the treatment of 4 with carbodiimides (RN) 2 C gives four-membered thorium metallaheterocycles [η 5 -1,3- (11), i Pr ( 12)] in 85% and 78% yields, respectively (Scheme 6). We propose that (RN) 2 C initially reacts with 4 via a [2 + 2] cycloaddition, which induces KCl loss and yields a four-membered thorium metallaheterocycle that converts to 11 and 12 by [1,3]-Th migration (Scheme 6).…”

Isocyanate Insertion into a La–P Phosphide Bond: A Versatile Route to Phosphaureate-Bridged Heterobimetallic Lanthanide–Coinage-Metal Complexes

“…In 2018, Walensky and co-workers presented the addition of tert -butylnitrile across one of the Th–P bonds of a thorium(IV) bis(mesitylphosphido) complex with concurrent proton transfer from phosphorus to nitrogen ( Scheme 2 ). 68 Intriguingly, the newly formed phosphaamidinate ligand could be selectively deprotonated by a strong base such as KHMDS in the presence of 2,2,2-cryptand, resulting in a rare example of an end-on-coordinated dianionic aza-1-phosphaallyl ligand.…”

“…Recently, our group has reported the synthesis of primary phosphido complexes (PN) 2 Ln(PHMes) (Ln = La, Lu) supported by a bidentate, monoanionic anilidophosphine ligand ( N -(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide, abbreviated PN – ). 76 Intrigued by the examples of Walensky 68 and Zhou, 75 we were interested if our complex (PN) 2 La(PHMes) ( 1 ) is prone to undergo a similar insertion chemistry with heterocumulenes. This type of reactivity has already been reported for group IV and actinide primary phosphido complexes 64 , 71 but is virtually nonexistent for lanthanides.…”