Reactivity of bridged pentelidene complexes with isonitriles: a new way to pentel-containing heterocycles

The reaction of [Cp*E{W(CO)5 }2 ] (E=P (1 a), As (1 b); Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) with isonitriles RNC (R=tBu, cyclohexyl (Cy), nBu) depends on the steric demand of the substituent at the isonitrile as well as on the stoichiometry of the starting materials. With tBuNC only the Lewis acid/base adducts [Cp*E{W(CO)5 }2 (CNtBu)] (E=P (2 a), As (2 b)) are formed. The use of Cy and n-butylisonitrile leads first to the formation of the Lewis acid/base adduct, but only at low temperatures. At ambient temperatures, a rearrangement occurs and bicyclo[3.2.0]heptane derivatives of the type [{C(Me)C(CH2 )C(Me)C(Me)C(Me)}C(NR)- E{W(CO)5 }2 ] (E=P, As; R=Cy, nBu) (3 a-Cy, 3 b-Cy, 3 a-nBu and 3 b-nBu) are obtained. The use of a further equivalent of isonitrile results in products revealing two new structural motifs, the four-membered ring derivatives [C(Cp*)N(R)C(NR)E{W(CO)5 }2 ] (4: E=P, As; R=Cy, nBu) and the bicyclic complexes [[{C(Me)C- (CH2 )C(Me)C(Me)C(Me)}C(NR)2 - E{W(CO)5 }2 ] (5: E=As; R=Cy). The reaction pathway depends on the substituent at the isonitrile. By treatment of 1 a with two equivalents of CyNC only a 2H-1,3-azaphosphet complex 4 a-Cy (E=P; R=Cy) is formed. Treatment of 1 b with two equivalents of CyNC exclusively leads to the complex 5 b-Cy (E=As; R=Cy). Treatment of 1 a with two equivalents of nBuNC results in a mixture of complexes, the 2H-1,3-azaphosphet 4 a-nBu (E=P; R=nBu) and the bicyclic complex 5 a-nBu (E=P; R=nBu). For the arsenidene complex 1 b a mixture of the 2H-1,3-azarsete complex 4 b-nBu (E=As; R=nBu) and the bicyclic complex 5 b-nBu (E=P, As; R=Cy, nBu) is obtained. Complex 4 b-nBu is the first example of a 2H-1,3-azarsete complex. All products have been characterized by using mass spectrometry, NMR spectroscopy, and X-ray diffraction analysis.