Isomeric forms of heavier main group hydrides: experimental and theoretical studies of the [Sn(Ar)H]2 (Ar = terphenyl) system.
Isomeric forms of heavier main group hydrides: experimental and theoretical studies of the [Sn(Ar)H]2 (Ar = terphenyl) system.
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DOI：
10.1021/ja076453m
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发表时间：
2007-12
影响因子：
15
通讯作者：
E. Rivard;R. Fischer;R. Wolf;Yang Peng;W. Merrill;N. Schley;Zhongliang Zhu;L. Pu;J. Fettinger;S. Teat;Isreal Nowik;R. Herber;Nozomi Takagi;S. Nagase;P. Power
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文献类型：
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作者：
E. Rivard;R. Fischer;R. Wolf;Yang Peng;W. Merrill;N. Schley;Zhongliang Zhu;L. Pu;J. Fettinger;S. Teat;Isreal Nowik;R. Herber;Nozomi Takagi;S. Nagase;P. Power
一般形式的对称二价锡(II)氢化物[(4-X-Ar‘)Sn(Mu-H)]2(4-X-Ar’=C6H2-4-X-2，6-(C6H3-2，6-iPr2)2；X=H、MeO、TBU和SiMe3；3，5-iPr2-Ar*=3，5-iPr2-C6H-2，6-(C6H2-2，4，6-iPr3)2)。它们或者通过相应的芳基氯化锡(II)前体ArSnCl与LiBH4或iBu2AlH(Dibal)直接还原，或者通过芳基锡(II)酰胺、ArSnNMe2和BH3.THF之间的跨金属反应而制备。化合物2、6、10和14以橙色固体的形式获得，并在固相中具有中心对称的二聚体结构，长的锡…锡分离在3.05到3.13A之间。更受阻碍的锡(II)氢化物16结晶为深蓝色固体，具有不寻常的，形式上的混价结构，其中存在一个长的锡-锡键[锡-锡=2.9157(10)A]，并且两个氢原子与一个锡原子结合。X-射线结晶学不能确定化合物16中的锡-氢原子的位置，但补充性穆斯堡尔研究证实了16中存在二价和四价锡中心。光谱研究(IR、UV-Vis和核磁共振)表明，在溶液中，化合物2、6、10和14主要是具有锡-氢-锡桥的二聚体。相反，受阻较大的氢化物16和以前报道的(Ar*SNH)2(17)(Ar*=C6H3-2，6-(C6H2-2，4，6-iPr3)2)在溶液中主要采用非对称结构ArSnSn2Ar。进行了详细的理论计算，包括计算了已报道的氢化物的各种可能的异构体和相关模型物种的UV-Vis和IR光谱。这些结果表明，相对于中心对称异构体[ArSn(Mu-H)]2，空间位阻的增加有利于不对称形式的ArSnSn(H)2AR，这是由于TiN上配体间夹角的扩大，从而降低了三苯基之间的空间斥力。
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 (Ar*SnH)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.