Synthesis, characterization, and reactivity of actinide complexes bearing An-E bonds (An = Th, U; E = P, As)
Authors:   , Tarlton Michael Lloyd 
Published: May 2022

Organoactinide complexes bearing An-E (An = Th, U; E = P, As) bonds were synthesized and reactivity studies were performed with various unsaturated and industrially/environmentally relevant small molecules in an effort to elucidate further information regarding their functionalization, and to expand the currently limited knowledge on actinide phosphido/arsenido chemistry. Reaction of isostructural, primary pnictido complexes of the form (C5Me5)2An[P(H)Mes]2 exhibited insertion-type reactivity with tBuCN, tBuNC, CO2 and CO. The products with CO2 and tBuNC were isostructural between Th, and U, resulting in the bis(phosphinocarboxylato), and phosphaazaallene complexes, (C5Me5)2An[[kappa]2-(O,O)-O2CP(H)Mes]2, and (C5Me5)2An[(CNtBu)([eta]2-(C,N)-tBuNC=PMes)]2, respectively. Divergent reactivity was observed with tBuCN, and CO, producing the U(IV) bis(ketimido) complex (C5Me5)2U[[kappa]2-(N,N)-(N=CtBu)2(PMes)]2, formed via elimination of free H2PMes, and (C5Me5)2U[([kappa]2-(O,O)-O2C(PMes)C(H)P(H)Mes], for which mechanistic analysis (DFT) attributed the difference to lower the acidity of the U-center to that of Th. Reaction of (C5Me5)2Th[P(H)Mes]2 with MN(SiMe3)2 (M = Na, K, Rb, Cs) leads to deprotonation of the P-H proton, leading to formation of alkali-metal phosphinidiide complexes of the form {(C5Me5)2Th[[mu]2-P(Mes)][[mu]2-P(H)Mes]M(L)n}2 (L = THF, Et2O), where computational (DFT) analysis and 31P NMR spectroscopy suggests significant Th-P multiple bond character. Reaction of (C5Me5)2Th[P(H)Mes]2 with CuMes in a 2:3 molar ratio leads to the formation of the bimetallic cluster, (C5Me5)2Th[([mu]2-PH(Mes)P(Mes)]Cu}2Cu[[mu]2-PH(Mes)]. Reaction of (C5Me5)2ThMe2 with H2PMes in a 2:1 molar ratio leads to the formation of the T-shaped, bridging Th-phosphinidiide, [(C5Me5)2Th]2(P-2,6-CH2C6H2-4-CH3) as a result of C-H bond activation at the o-CH3 groups on the mesityl ring. Computational analysis (DFT) of the mechanism reveals that it progresses a different mechanism than that of the previously published and analogous reaction with H2PTipp (Tipp = 2,4,6-triisopropylphenyl), yielding [(C5Me5)2Th]2([mu]2-P[(2,6-CH2CHCH3)2-4-iPrC6H2]. A comparative study was carried out in which isostructural Th and U complexes bearing bonds to P and As was conducted, yielding primary bis(pnictido) complexes of the form (C5Me5)2An[E(H)Mes]2, dipnictido complexes of the form (C5Me5)2Th([eta]2-E2Mes2), bridging bis(pnictinidiide) complexes of the form [(C5Me5)2U]2([mu]2-AsMes)2 (with the exception of An = Th, E = P, which underwent C-H bond activation to form {(C5Me5)2Th[[mu]2-P(H)(2,4-Me2C6H2-6-CH2)]}2), and the terminal, U-phosphinidene complex, (C5Me5)2U(=PMes)OPPh3. Attempts were made to generate terminal arsinidene complexes from the bridging bis(arsinidiide) complexes by reaction with 2 molar equivalents of OPPh3, but the oxo group was abstracted in the case of the Th-arsinidiide with concomitant elimination of 0.5 Mes-As=As-Mes, resulting in the bridging oxo complex [(C5Me5)2Th]2([mu]2-AsMes)([mu]2-O). The analogous reaction between [(C5Me-5)2U]2([mu]2-AsMes)2 and OPPh3 results in reduction of the U(IV/IV) centers and concomitant coupling of the arsinidiide ligands to form the U(III/III) diarsenido/OPPh3 adduct ion pair, [(C5Me5)2U([eta]2-As2Mes2)][(C5Me5)2U(OPPh3)2]. Following this study, the An-diarsenido complexes were reacted with CO and isoelectronic analog, tBuNC, forming the adducts (C5Me5)2An([eta]2-As2Mes2)(CNtBu) and (C5Me5)2An([eta]2-As2Mes2)(CO). The latter complexes represent very are examples of characterizable carbonyl compounds of f elements.