Electron-rich diplatinum(0) metallocryptate promoting novel successive encapsulation of acidic hydrides
Electron-rich diplatinum(0) metallocryptate promoting novel successive encapsulation of acidic hydrides
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DOI：
10.1021/om049548v
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发表时间：
2004-12-06
期刊：
影响因子：
2.8
通讯作者：
Tanase, T
中科院分区：
文献类型：
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作者：
Goto, E;Usuki, M;Tanase, T
[Pt(XyINC)(4)](PF6)(2)与NaBH4在2,7-二（二苯基膦）1,8-萘啶（dpnapy）存在下反应，在伪d -3螺旋笼中得到具有紧密包裹钠离子的双铂(0)金属隐式酸盐[Pt2Na(mud -dpnapy)(3)(XylNC)(2)](PF6) （4a; XylNC = 2,6-二甲苯异氰酸酯）。配合物4a中的3个线性dpnapy配体由一个钠离子通过6个Na- n键结合，两个Pt-0（XyINC）片段通过3个Pt-P键覆盖在双三脚{(dpnapy)(3)Na}（+）单元的两端。每个富电子铂(O)中心采用具有18个价电子的四面体几何结构。以[Pd-3(XylNC)(6)]与dpnappy和NaPF6反应制备了类似的二钯(0)配合物[Pd2Na(mu- dpnappy)(3)(XylNC)(2)](PF6) （4b）。配合物4a、b的末端异氰化物配体很容易被CO （1atm）取代，得到[M2Na(mu-dpnapy)(3)(CO)(2)](PF6) (M = Pt （4c), Pd (4d)）。在H+离子的存在下，富电子的双铂金属隐体4a有趣地表现出质子作为铂结合氢化物的连续封装，导致形成[Pt2Na(H)(mu-dpnapy)(3)(XylNC)(2)](PF6)(2)(5)和[Pt2Na(H)(2)(mu-dpnapy)(3)(XylNC)(2)] (PF6)(3)(6)。在调控量的HPF6存在下，从[Pt-3(XylNC)(6)]与dpnappy和NaPF6的交替反应中分离到配合物5和6。虽然5和6的结构与4a非常相似，但配合物5和6中的{Pt(PCN)(3)Na}框架分别捕获了一个和两个氢化物。在异氰化物的相反位置，氢化物附着在Pt中心上，Pt原子向三角-双锥体几何方向轻微变形。5的结构是不对称的，氢化物固定在铂中心，即使在溶液中也没有观察到氢化物的任何位置交换行为。5中的氢化物包覆将内部遇到的铂原子拖拽约0.17埃，并在中心Na离子周围产生轻微但明显的畸变，NO侧的平均Na- n距离为2.42埃，PtH侧的平均Na- n距离为2.54埃。氢化物包封引起的结构扭曲可能影响了其他Pt中心的反应性，从而稳定了5的不对称结构。对4a、5和6进行了电化学测量，发现配合物4a在E-pa(1) = -0.14 V （vs Ag/Ag+）和0.15 V下经历了两个不可逆的单电子氧化过程，对应于Pt-2(0) -> (PtPtI)-Pt-0 -> Pt-2(I)，并伴有一些结构变化，氢化物包封使Pt中心在5和6中无氧化还原活性，而Pt-0(PtH) -> Pt-I(PtH)(5)和（PtH）(2)是氧化还原沉默的(6)。
Reaction of [Pt(XyINC)(4)](PF6)(2) with NaBH4 in the presence of 2,7-bis(diphenylphosphino)1,8-naphthyridine (dpnapy) afforded a diplatinum(0) metallocryptate with a tightly encapsulated sodium ion in a pseudo-D-3 helical cage, [Pt2Na(mu-dpnapy)(3)(XylNC)(2)](PF6) (4a; XylNC = 2,6-xylyl isocyanide). The three linear dpnapy ligands in complex 4a are bundled by a sodium ion through six Na-N bonds, and two Pt-0(XyINC) fragments cap each end of the double-tripodal {(dpnapy)(3)Na}(+) unit through three Pt-P bonds. Each electron-rich platinum(O) center adopts a tetrahedral geometry with 18 valence electrons. An analogous dipalladium(0) complex, [Pd2Na(mu-dpnapy)(3)(XylNC)(2)](PF6) (4b), was prepared by reaction of [Pd-3(XylNC)(6)] with dpnapy and NaPF6. The terminal isocyanide ligands of complexes 4a,b were readily replaced by CO (1 atm) to give [M2Na(mu-dpnapy)(3)(CO)(2)](PF6) (M = Pt (4c), Pd (4d)). In the presence of H+ ions, the electron-rich diplatinum metallocryptate 4a interestingly demonstrated successive encapsulation of protons as platinum-bound hydrides, resulting in the formation of [Pt2Na(H)(mu-dpnapy)(3)(XylNC)(2)](PF6)(2) (5) and [Pt2Na(H)(2)(mu-dpnapy)(3)(XylNC)(2)] (PF6)(3) (6). Complexes 5 and 6 were isolated from alternative reactions of [Pt-3(XylNC)(6)] with dpnapy and NaPF6 in the presence of regulated amounts of HPF6. Whereas the structures of 5 and 6 are closely similar to that of 4a, one and two hydrides are trapped into the small room comprised of the {Pt(PCN)(3)Na} framework in complexes 5 and 6, respectively. The hydride attached to the Pt center at the opposite site of isocyanide with the Pt atom deformed slightly toward trigonal-bipyramidal geometry. The structure of 5 is asymmetric with the hydride fixed onto a platinum center, and any site-exchange behavior of the hydride was not observed even in solution. The hydride encapsulation in 5 drags the encountered platinum atom inside by ca. 0.17 Angstrom and causes slight but appreciable distortion around the central Na ion with an average Na-N distance of 2.42 Angstrom for the NO side and 2.54 Angstrom for the PtH side. The structural distortion caused by the hydride encapsulation might have influenced the other Pt center to be less reactive and stabilize the asymmetric structure of 5. Electrochemical measurements for 4a, 5, and 6 were performed to reveal that complex 4a underwent two irreversible one-electron oxidation processes at E-pa(1) = -0.14 V (vs Ag/Ag+) and 0.15 V, corresponding to Pt-2(0) --> (PtPtI)-Pt-0 --> Pt-2(I) with some concomitant structural changes, and the hydride encapsulation made the Pt center redox inactive in 5 and 6, as Pt-0(PtH) --> Pt-I(PtH) (5) and (PtH)(2) were redox silent (6).