The novel complexes M[O(R)PhCH{CH=N(tBu)}N(tBu)](2) [M = Zr, R = Me (4a), R = Ph (4b) and M = Hf, R = Me (5a), R = Ph (5b)] have been prepared in almost quantitative yield by reaction of (tBu-DAD)(2)Zr (1) and (tBu-DAD)(2)Hf(2) [tBu-DAD = (tBu)N=CHCH=N(tBu)] with 2 equiv of the ketones MeCOPh (3a) or PhCOPh (3b). The reaction proceeds via a 1,3-dipolar cycloaddition of the C=O bond across the M-N-C unit of the DAD complexes. The molecular structures of the complexes 4a and 5b have been determined by a single-crystal X-ray diffraction study (4a, triclinic, space group P (1) over bar; a 10.395(2) Angstrom, b = 10.865(2) Angstrom, c = 16.842(3) Angstrom, alpha = 93.80(3)degrees, beta = 99.84(3)gamma, gamma = 106.12(3)degrees, V = 1787.4(6) Angstrom(3), Z = 2, R1 = 0.035 (wR2 = 0.101) for 6963 reflections with I > 2 sigma(T); 5b, monoclinic, space group P2(1)/c, a = 19.961(4) Angstrom, b = 10.482(2) Angstrom, c = 20.150(4) Angstrom, beta = 91.30(1)degrees, V = 4215(1) Angstrom(3), Z = 4, R1 = 0.036 (wR2 = 0.097) for 4650 reflections with I > 2 sigma(I)). The metal atoms in 4a and 5b adopt a pseudooctahedral coordination sphere consisting of four nitrogen and two oxygen atoms. The distortion is a consequence of the [2.2.1] bicyclic structure of the newly formed tridentate ligands which are not able to span three regular octahedral positions.