Zheng Zhaoyu, Pavlov Julius, Wei Yang, Zhang Yong, Attygalle Athula B
Center for Mass Spectrometry, Department of Chemistry and Chemical Biology, Stevens Institute of Technology, Hoboken, New Jersey 07030, United States.
ACS Omega. 2018 Mar 23;3(3):3440-3452. doi: 10.1021/acsomega.7b01518. eCollection 2018 Mar 31.
Metal-hydride anions of main group elements, such as BaH and InH , were generated by dissociating formate adducts of the respective metal formates. Upon activation, these adducts fragment by formate-ion ejection or by decarboxylation. For adducts of alkali-metal formates, the formate-ion ejection is the preferred pathway, whereas for those of alkaline-earth and group 13-15 metals, the expulsion of CO is the more favorable pathway. Decarboxylation is deemed to yield a metal-hydrogen bond presumably by a hydride transfer to the metal atom. For example, the decarboxylation of Al(η-OCOH) and Ga(η-OCOH) generated AlH and GaH , respectively. The initial fragment-ion with a H-M bond formed in this way from adducts of the heavier metals of group 13 (Ga, In, and Tl) undergo a unimolecular reductive elimination, ascribable to the "inert-pair" effect, to lower the metal-ion oxidation state from +3 to +1. As group 13 is descended, the tendency for this reductive elimination process increases. PbH , generated from the formate adduct of lead formate, reductively eliminated H to form PbH, in which Pb is in oxidation state zero. In the energy-minimized structure [H-Pb(η-H)], proposed as an intermediate for the process, a H molecule is coordinated with PbH as a dihapto ligand. The formate adducts of strontium and barium produce monoleptic ions such as [M(0)(η-OCH)], in which the formate ion is chelated to a neutral metal atom. The bismuth formate adduct undergoes a double reductive elimination process whereby the oxidation state of Bi is reduced from +3 to +1 and then to -1. Upon activation, the initially formed [H-Bi-H] ion transforms to an anionic η-H complex, which eliminates dihydrogen to form the bismuthide anion (Bi).
主族元素的金属氢化物阴离子，如BaH和InH，是通过分解相应金属甲酸盐的甲酸盐加合物生成的。活化后，这些加合物通过甲酸根离子的排出或脱羧作用而裂解。对于碱金属甲酸盐的加合物，甲酸根离子的排出是首选途径，而对于碱土金属和第13 - 15族金属的加合物，CO的排出是更有利的途径。脱羧作用被认为可能通过氢化物转移到金属原子上而产生金属 - 氢键。例如，Al(η - OCOH)和Ga(η - OCOH)的脱羧分别生成了AlH和GaH。以这种方式从第13族较重金属（Ga、In和Tl）的加合物中形成的带有H - M键的初始碎片离子会发生单分子还原消除反应，这归因于“惰性电子对”效应，从而使金属离子的氧化态从 +3降低到 +1。随着第13族元素原子序数的增加，这种还原消除过程的趋势增强。由甲酸铅的甲酸盐加合物生成的PbH，通过还原消除H形成PbH，其中Pb的氧化态为零。在作为该过程中间体提出的能量最小化结构[H - Pb(η - H)]中，一个H₂分子作为双齿配体与PbH配位。锶和钡的甲酸盐加合物产生单配位离子，如[M(0)(η - OCH)]，其中甲酸根离子与中性金属原子螯合。甲酸铋加合物经历双重还原消除过程，由此Bi的氧化态从 +3降低到 +1，然后再降低到 -1。活化后，最初形成的[H - Bi - H]离子转变为阴离子η - H络合物，该络合物消除氢气形成铋化物阴离子（Bi⁻）。
