Tungsten Phosphine Polyhydrides

Submitted by GREGORY G. HLATKY and ROBERT H. CRABTREE Checked by KIMBERLY A. KUBAT-MARTIN and G. J. KUBAS  

Transition metal polyhydrides have several features that are currently attracting considerable interest. For example, some examples have been found to have hydrides bound in a nonclassical t/ -H2 fashion, e.g.. 

65 mmol) (Aldrich) is added slowly with a syringe over 10 min. The deep red homogeneous mixture is stirred at room temperature for 12 h. 

2-bis(diphenylphosphino)ethane complex can be prepared in an almost identical way, but it is recrystallized from a minimum amout of hot benzene by precipitation with ethanol in 50% yield. 

The physical and solubility properties of the tungsten complex are similar to those of the molybdenum analog, except that it is less photosensitive. The HNMR spectrum at room temperature (toluene-tig) shows this complex to be stereochemically rigid, but at 60 °C, a binomial quintet is observed at d — 1.72 for the W—H protons ( ph = 31 Hz). 

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Semenenko and coworkers have proposed a method for the synthesis of tungsten and molybdenum polyhydride complexes, [M(H)4(PR3)4] (M = W, Mo PR3 = phosphine or phosphite). The method involves ion exchange between [Md ] and Ca[BH4l2 in dimethoxyethane and results in the formation of the borohydride complexes, [M(ti2-BH4)J, which were identified in situ by IR spectroscopy. Addition of PR3 leads to the decomposition of the i]2-borohydride complexes and isolation of the polyhydrides, [M(H)4(PR3)4]. 

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