Rivard Eric, Fischer Roland C, Wolf Robert, Peng Yang, Merrill W Alexander, Schley Nathan D, Zhu Zhongliang, Pu Lihung, Fettinger James C, Teat Simon J, Nowik Isreal, Herber Rolfe H, Takagi Nozomi, Nagase Shigeru, Power Philip P
Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California, 95616, USA.
J Am Chem Soc. 2007 Dec 26;129(51):16197-208. doi: 10.1021/ja076453m. Epub 2007 Dec 4.
A series of symmetric divalent Sn(II) hydrides of the general form [(4-X-Ar')Sn(mu-H)]2 (4-X-Ar' = C6H2-4-X-2,6-(C6H3-2,6-iPr2)2; X = H, MeO, tBu, and SiMe3; 2, 6, 10, and 14), along with the more hindered asymmetric tin hydride (3,5-iPr2-Ar*)SnSn(H)2(3,5-iPr2-Ar*) (16) (3,5-iPr2-Ar* = 3,5-iPr2-C6H-2,6-(C6H2-2,4,6-iPr3)2), have been isolated and characterized. They were prepared either by direct reduction of the corresponding aryltin(II) chloride precursors, ArSnCl, with LiBH4 or iBu2AlH (DIBAL), or via a transmetallation reaction between an aryltin(II) amide, ArSnNMe2, and BH3.THF. Compounds 2, 6, 10, and 14 were obtained as orange solids and have centrosymmetric dimeric structures in the solid state with long Sn...Sn separations of 3.05 to 3.13 A. The more hindered tin(II) hydride 16 crystallized as a deep-blue solid with an unusual, formally mixed-valent structure wherein a long Sn-Sn bond is present [Sn-Sn = 2.9157(10) A] and two hydrogen atoms are bound to one of the tin atoms. The Sn-H hydrogen atoms in 16 could not be located by X-ray crystallography, but complementary Mössbauer studies established the presence of divalent and tetravalent tin centers in 16. Spectroscopic studies (IR, UV-vis, and NMR) show that, in solution, compounds 2, 6, 10, and 14 are predominantly dimeric with Sn-H-Sn bridges. In contrast, the more hindered hydrides 16 and previously reported (ArSnH)2 (17) (Ar = C6H3-2,6-(C6H2-2,4,6-iPr3)2) adopt primarily the unsymmetric structure ArSnSn(H)2Ar in solution. Detailed theoretical calculations have been performed which include calculated UV-vis and IR spectra of various possible isomers of the reported hydrides and relevant model species. These showed that increased steric hindrance favors the asymmetric form ArSnSn(H)2Ar relative to the centrosymmetric isomer [ArSn(mu-H)]2 as a result of the widening of the interligand angles at tin, which lowers steric repulsion between the terphenyl ligands.
一系列通式为[(4-X-Ar')Sn(μ-H)]₂的对称二价氢化锡(II)（4-X-Ar' = C₆H₂-4-X-2,6-(C₆H₃-2,6-iPr₂)₂；X = H、MeO、tBu和SiMe₃；分别对应化合物2、6、10和14），以及位阻更大的不对称氢化锡(3,5-iPr₂-Ar*)SnSn(H)₂(3,5-iPr₂-Ar*)（16）（3,5-iPr₂-Ar* = 3,5-iPr₂-C₆H-2,6-(C₆H₂-2,4,6-iPr₃)₂）已被分离和表征。它们可通过用LiBH₄或二异丁基氢化铝（DIBAL）直接还原相应的芳基氯化锡(II)前体ArSnCl来制备，或者通过芳基锡(II)酰胺ArSnNMe₂与BH₃·THF之间的金属转移反应来制备。化合物2、6、10和14以橙色固体形式获得，在固态时具有中心对称的二聚体结构，Sn…Sn长间距为3.05至3.13 Å。位阻更大的氢化锡(II) 16以深蓝色固体形式结晶，具有不寻常的形式上的混合价结构，其中存在一个长的Sn-Sn键[Sn-Sn = 2.9157(10) Å]，并且两个氢原子与其中一个锡原子相连。16中的Sn-H氢原子无法通过X射线晶体学确定位置，但补充的穆斯堡尔研究确定了16中存在二价和四价锡中心。光谱研究（红外、紫外可见和核磁共振）表明，在溶液中，化合物2、6、10和14主要以具有Sn-H-Sn桥的二聚体形式存在。相比之下，位阻更大的氢化物16和先前报道的(ArSnH)₂（17）（Ar = C₆H₃-2,6-(C₆H₂-2,4,6-iPr₃)₂）在溶液中主要采用不对称结构ArSnSn(H)₂Ar。已经进行了详细的理论计算，其中包括所报道氢化物的各种可能异构体以及相关模型物种的计算紫外可见和红外光谱。结果表明，由于锡原子处配体间角度的增大，空间位阻增加有利于不对称形式ArSnSn(H)₂Ar相对于中心对称异构体[ArSn(μ-H)]₂，这降低了三联苯配体之间的空间排斥。
