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首页> 外文期刊>Chemistry: A European journal >Nitrido Dimers and Trimers of Tungsten Supported by tBuMe_2SiO and CF_3Me_2CO Ligands, Respectively. Factors Influencing the Reductive Cleavage of Nitriles by Tungsten - Tungsten Triple Bonds and An Analysis of the Structure of the Cyclotrimer
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Nitrido Dimers and Trimers of Tungsten Supported by tBuMe_2SiO and CF_3Me_2CO Ligands, Respectively. Factors Influencing the Reductive Cleavage of Nitriles by Tungsten - Tungsten Triple Bonds and An Analysis of the Structure of the Cyclotrimer

机译：分别由tBuMe_2SiO和CF_3Me_2CO配体负载的钨的氮化物二聚体和钨三聚体。钨-钨三键对腈还原裂解的影响因素及环三聚体的结构分析。

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摘要

[W_2(OR)_6] compounds (R = tBuMe_2Si and CF_3Me_2C) are shown to react reversibly iwth nitriles (MeCN and ArCN) in [D_8]toluene to give [W_2(OR)_6L_2] compounds (L = nitrile). For MeCN the enthalpy of adduct for mation for [M_2(OCCF_3Me_2)_6] favors tungsten over molybdenum : #DELTA#Hdeg = 22(1) kcalmol~(-1) (M = Mo) vs. #DELTA#Hdeg = -26(1) kcalmol~(-1) (M = W), while for both metals the #DELTA#Sdeg values were about - 80 eu. From an ~15N NMR line-shape analysis the activation parameters for adduct formation are calcualted to be #DELTA#H~(not=) = +24(2) kcalmol~(-1) and #DELTA#S~(not=) = 36(6) eu for M=W and #DELTA#H~(not=) = 19(2) kcalmol~(-1) and #DELTA#S~(not=) = -38(6) eu for M=Mo. Adduct formation is less favored for benzonitrile with #DELTA#Hdeg = -16(1) kcalmol~(-1) for the formation of [W_2(OCMe_2CF_2)_6(NCC_6H_5)_2]. However, the reductive cleavage of PhC(ident to)N is favored kinetically over meC(ident to)N and only occurs for M = W. For reactions between [W_2(OCCF_3Me_2)_6] ad PhCN (10,20 and 30 equivalents of PhCN) the rate is retarded with increasing nitrile concentration. The activated species is proposed to be a monoadduct [W_2(OR)_6(#mu#-NCPh)]. The products of the cleavage are [NW(OR)_3]_n and MeC(ident to)CMe or ArC(ident to)CAr for MeC(ident to)N and PhC(ident to)N, respectively, as determined by ~13C and ~15N labeling studies. For R = tBuMe_2Si a dimeric structure is obtianed with terminal nitride ligands and bridging OSitBuMe_2 ligands. For R = CCF_3Me_2, a cyclotrimer exists both in solution and the solid state, with a planar W_3N_3 ring with alternating short and long W-N distances. The structure of the model compound [(OH)_3WN]_3 has bee investigated by DFT (B3LYP) calculations. The short -long alternating WN bond lengths of the ring are well reproduced and are attributed to the preference for the OR groups to occupy two equatorial and one axial site of the trigonal bipyramid at each W center. Models of transition states were studied and support the absence of site exchange at each tungsten; this would have led to an interchange of the short and long W-N bonds. These findings are discussed in terms of the earlier predictions of Hoffmann et al. and the experimetnal findings of other workers for d(deg) metal nitrides of formula [L_nMN]_x. The cell parameters for [(CF_3Me_2CO)_3WN]_3 at -169deg C are: a = 22.481(5), b = 11.367(2), c = 22.573(2) A, #beta# = 94.6(1) and space group P1_1/c.
机译：[W_2（OR）_6]化合物（R = tBuMe_2Si和CF_3Me_2C）与[D_8]甲苯中的腈（MeCN和ArCN）可逆反应，得到[W_2（OR）_6L_2]化合物（L =腈）。对于MeCN，[M_2（OCCF_3Me_2）_6]的加成焓对钨比钼有利：＃DELTA＃Hdeg = 22（1）kcalmol〜（-1）（M = Mo）vs.＃DELTA＃Hdeg = -26 （1）kcalmol〜（-1）（M = W），而两种金属的＃DELTA＃Sdeg值约为-80 eu。通过〜15N NMR线形分析，计算出加合物形成的活化参数为＃DELTA＃H〜（not =）= +24（2）kcalmol〜（-1）和＃DELTA＃S〜（not =）对于M = W，= 36（6）eu，对于M，＃DELTA＃H〜（not =）= 19（2）kcalmol〜（-1），对于M，＃DELTA＃S〜（not =）= -38（6）eu = Mo。对于[W_2（OCMe_2CF_2）_6（NCC_6H_5）_2]的形成，对于＃DELTA＃Hdeg = -16（1）kcalmol〜（-1）的苄腈，加合物的形成不太有利。但是，PhC（等同于）N的还原裂解在动力学上优于meC（等同于）N，并且仅在M = W时发生。对于[W_2（OCCF_3Me_2）_6]和PhCN之间的反应（10,20和30当量的随着腈浓度的增加，该速率受阻。提议的活化物种是单加合物[W_2（OR）_6（＃mu＃-NCPh）]。裂解的产物分别为[NW（OR）_3] _n和MeC（等同于）CMe或ArC（等同于）CAr的MeC（等同于）N和PhC（等同于）N，由〜13C确定和〜15N标记研究。对于R ＝ tBuMe_2Si，二聚体结构被末端氮化物配体和桥接OSitBuMe_2配体所构型。对于R = CCF_3Me_2，在溶液和固态下均存在环三聚体，且平面W_3N_3环具有短的W-N距离和长的W-N距离。通过DFT（B3LYP）计算研究了模型化合物[（OH）_3WN] _3的结构。该环的短-长交替WN键长很好地再现，并且归因于优选OR基团在每个W中心占据三角双锥体的两个赤道和一个轴向位点。研究了过渡态模型，并支持在每个钨上不存在位交换。这将导致短期和长期W-N键互换。这些发现是根据Hoffmann等人的早期预测进行讨论的。以及其他工人对式[L_nMN] _x的d（deg）金属氮化物的实验结果。 -[[CF_3Me_2CO）_3WN] _3在-169°C的像元参数为：a = 22.481（5），b = 11.367（2），c = 22.573（2）A，＃beta＃= 94.6（1）和空间组P1_1 / c。

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