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W(NPh)[o-(Me3SiN)2C6H4](CH2CMe3)2, 2h, is quantitatively converted to a new metallacyclopentane complex, W(CH2CH2CH2CH2)(NPh)[o-(Me3SiN)2C6H4], 4, upon the addition of ethylene at T > 70 °C. The complex W(CH2CH2CH2CH2)(NPh)[o-(Me3SiN)2C6H4], 4, was also formed by the transmetalation reaction of W(NPh)[o-(Me3SiN)2C6H4](Cl)2 with the corresponding Grignard reagent, BrMg(CH2)4MgBr, and also when W(NPh)[o-(Me3SiN)2C6H4](PMe3)(C(H)t-Bu), 3, reacts with ethylene. Mechanistic studies suggest that 2h and 3 react with ethylene through a common base-free alkylidene intermediate which undergoes metathesis with ethylene and then generates a W(IV) intermediate which is converted to 4 by coupling two molecules of ethylene. This reaction is a deactivation pathway when 3 is used as an olefin metathesis catalyst for terminal olefins because ethylene is generated during the reaction. The tungsten(IV) complex W(NPh)[o-(Me3SiN)2C6H4](PMe3)2(η2-C2H4), 5, was observed during the reaction between 3 and ethylene. Complex 5 can also be synthesized from the diethyl complex W(NPh)[o-(Me3SiN)2C6H4](CH2CH3)2, 2b, in the presence of PMe3. Addition of excess ethylene to 5 gives 4. The X-ray structure of 4 was determined.

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The complexes [(TMS)2pda](NPh)WR2 ((TMS)2pda = o-(Me3SiN)2C6H4}2-; R = CH3 (1), CH2CMe3 (4)) react with tBuNC to form the octahedral monoadducts [(TMS)2pda](NPh)WR2(CNtBu) (1a and 4a). 1a is observed only at low temperature, while 4a can be isolated. Both 1a and 4a react with tBuNC to form the corresponding trigonal bipyramidal bis(η2-imino-acyl) species [(TMS)2pda](NPh)W[η2-(tBu)NCR]2 (R = CH3 (2), CH2CMe3 (5)), which have been isolated and characterized. Compound 2 isomerizes upon heating to the square pyramidal metallacycle [(TMS)2pda](NPh)W[(tBu)NC(CH3)C(CH3)N(tBu)] (3), which has been isolated as a red solid. X-ray crystal structures have been obtained for compounds 2 and 3. Crystals of 2 are orthorhombic, space group P212121, with a = 9.1175(3) Å, b = 17.9587(5) Å, c = 20.9435(6) Å, and Z = 4. Compound 2 has trigonal bipyramidal geometry with the imido N and one amido N in axial positions. Crystals of 3 are monoclinic, space group C2/c, with a = 35.1302(9) Å, b = 12.6459(2) Å, c = 16.2386(6) Å, β = 112.021(3)°, and Z = 8. 3 has distorted square pyramidal geometry with the imido moiety in the apical position.