Phosphanide terminal

Whereas at 253 K only the monomeric molecule is detectable, at 283 K a small signal arises from the dimeric species (Fig. 2). At 313 K coalescence is observed between these two species, llirthermore, an intramolecular exchange reaction of the terminal and the bridging phosphanide ligands of the dimer broadens the singlets. The latter process is fast on the NMR time scale. The spectroscopic data are compared in Table 1. For the barium derivative shown in Fig. 3 the bicyclic structure has been proven by the small Vp p coupling of 6.7 Hz at 213 K which leads to a quartet for... 

The size of the trialkylsilyl groups determines the appearance of the dimeric molecule Thus, the dimethyl-i-propylsilyl substituent enforces a monocyclic dimeric barium bis(phosphanide) with two terminal and two bridging phosphanide ligands (Fig. 4) [4]. 

A further upheld shift ofAty=-180ppm to a value of =220ppm is observed, if the r-donor interaction of the amino substituent on phosphorus is retained, but the three-membered metallacycle is removed (replacement of one of the CpMoCCO) groups by a chlorine atom). The P=Mo double bond is now focused onto one molybdenum atom, rather then delocalized over two molybdenum atoms. The phosphorus moiety is a phosphanide rather than a phosphinidene species, and the phosphorus resonance at < p=220ppm is well in keeping with those of terminal phosphanides. 

The two complexes depicted in Fig. 7.25 look deceptively similar to the terminal phosphanide complex seen in Fig. 7.23, but they are indeed terminal phosphin-idenes, and the oxidation state of the group 6 metal is+lV and thus higher than the oxidation states of the examples in Fig. 7.22, which were+II. 

Fig. 7.23 chemical shift value of a terminal phosphanide complex... 

Hz). A a complex 29 with an agostic P-H bond was reported by Albinati et al. [95] as the protonation product of the corresponding neutral bis(/x-phosphanide)dipalladium complex. The 2e-3c interaction was suggested on the basis of 7(P,H) coupling constant of 151 Hz in comparison the values for the terminal P-H bond are 322-324 Hz. 

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