Structure metallacyclic

The diazaphosphane or aminoiminophosphane ligands with a NPN framework are another subclass of cyclophosphazenes. These compounds with both phosphorus in oxidation state (111) [104-110] and (V) [111-112] have been employed in the synthesis of four membered heterocycles and coordination chemistry with group 13 derivatives. Several complexes of trivalent phosphorus derivatives with both aluminum halide and alkyls are known as illustrated for 48 in Scheme 21 [113-119]. The structure determination of 48 confirms the formation of a four membered metallacycle [116, 117],... 

In contrast to known structures of related metallacycles e.g. in W2( -CSiMe3)2(0-i-Pr)4> e four-membered ring in 8 is folded along the Mn-Mn1 bond with an angle of 18.45° (Fig. 5). 

The a-osmiumdiazo compound 91 decomposes in a thermal reaction to yield the metallacyclic complex 93 (130). This resembles the electrophilic carbene insertion reaction forming OsCl(CO)2(PPh2C6H4CHCl) (PPh3) (77) (see Section V,D,2), and we suggest that a similar insertion reaction of an electrophilic, cationic osmium carbyne 92 is the key step in this transformation. An X-ray structure determination has confirmed the formulation of 93. 

Confirmation that the polymerizations proceed via metallacyclic intermediates was obtained by studying the ROMP of functionalized 7-oxanorbornadienes. These polymerize slower than their norbornene analogs, allowing NMR identification of the metallacyclobutane resonances and subsequent monitoring of ring opening to the first insertion product. In addition, the X-ray crystallographic structure of complex (212) has been reported.533... 

Fig. 1 X-ray crystal structures of Cp2M(dithiolene) complexes (a)d° Cp2Ti(dmit) (b)d1 Cp2V (bdt) (c) d2 Cp2Mo(dmit), showing the evolution of the metallacycle folding angle...

Uranium complexes analogous to these compounds were also described, but with the cot (cyclooctatetraene dianion) ligand rather than the Cp or Cp ones. Both the dianionic U(IV) [(cot)U(dddt)2]2 [47] and monoanionic U(V) [(cot)U(dddt)2] [48] complexes were isolated and structurally characterized (Fig. 5). Spectacular distortions of the US2C2 metallacycles were rationalized on the basis of DFT calculations, which reproduced the spectacular folding of the endo US2C2 metalla-cycle when the dianionic species undergoes an oxidation. 

A study of the reactions of butadiene, isoprene, or allene coordinated to nickel in a metallacycle, with carbonylic compounds, has been reported by Baker (example 11, Table IV). In the presence of phosphines, these metallacycles adopt a cr-allyl structure on one end and a ir-allyl structure on the other, as mentioned in Section II,A,1. The former is mainly attacked by aldehydes or electrophilic reagents in general, the latter by nucleophiles (C—H acids, see Table I, or amines, see Table IX). 

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