This study focuses on the viability of the carbazole-based Cbzdiphos PNP pincer ligand as a stabilizing element for group 4 metal complexes, and both the diphenylphosphino- and di-isopropylphosphino-substituted Cbzdiphos protioligands 1(Ph)H and 1(iPr)H were used. Treatment of the lithiated protioligands with the corresponding chlorido precursor compounds of the metals (titanium, zirconium, and hafnium) afforded the trichlorido complexes [(Cbzdiphos(iPr))MCl3] 2(iPr)M and [(Cbzdiphos(Ph))MCl3] 2(Ph)M (M = Ti, Zr, Hf), which were converted to the corresponding iodido complexes [(Cbzdiphos(iPr))MI3] 3(iPr)M and [(Cbzdiphos(Ph))MI3] 3(Ph)M (M = Ti, Zr, Hf) by reaction with an excess of trimethylsilyl iodide. Reaction of 2(iPr)Ti and 3(Ph)Ti with 1 equiv of dibenzyl magnesium tetrahydrofuran adduct led to the formation of the alkylidene complexes 4(iPr)Ti and 5(Ph)Ti, respectively, while the zirconium and hafnium complexes 2(iPr)Zr and 3(Ph)Zr/Hf formed the cyclometalated monoalkyl compounds [(Cbzdiphos(iPr)-CH)ZrBnCl] 6(iPr)Zr as well as [(Cbzdiphos(Ph)-CH)MBnX] 6(Ph)Hf (X = Cl) and 7(Ph)Zr/Hf (X = I) under analogous reaction conditions. On the other hand, stirring 2(Ph)Zr with 0.25 equiv of tetrabenzyl zirconium afforded [(Cbzdiphos(Ph))ZrBnCl2] (8(Ph)Zr), which contained the PNP ligand intact, while its alkylation with benzyl potassium led to the formation of the cyclometalated monobenzyl complex [(Cbzdiphos(Ph)-CH)ZrBnCl] (6(Ph)Zr). The remaining coordination site occupied by the halogenido ligand in the cyclometalated monobenzyl complexes [(Cbzdiphos-CH)MBnX] 6(iPr)Zr, 6(Ph)Zr/Hf, and 7(Ph)Zr/Hf was readily benzylated by treatment with benzyl potassium to afford the cyclometalated dibenzyl complexes [(Cbzdiphos-CH)MBn2] 9(iPr)Zr and 9(Ph)Zr/Hf. Further reaction of 9(Ph)Zr with an excess of benzyl potassium led to the formation of the anionic tribenzyl zirconium ate complex [(Cbzdiphos-CH)MBn3]K (10(Ph)Zr). Upon heating a solution of 8(Ph)Zr in the presence of 1 mol equiv of trimethyl phosphine, one of the ligand methylene groups was deprotonated, yielding the cyclometalated complex [(Cbzdiphos(Ph)-CH)ZrCl2(PMe3)] 11(Ph)Zr. Finally, reaction of 7(Ph)Zr with methylene triphenylphosphorane produced the ortho-metalated product [(Cbzdiphos(Ph)-CH)Zr(o-C6H4PPh2CH2)I] (12(Ph)Zr), which is characterized by a slightly puckered five-membered Zr-C(48)-P(3)-C(49)-C(50) metallacycle.

The cyclometalated monobenzyl complexes [(Cbzdiphos(R) -CH)ZrBnX] 1 (iPr) Cl and 1 (Ph) I reacted with dihydrogen (10 bar) to yield the η(6) -toluene complexes [(Cbzdiphos(R) )Zr(η(6) -tol)X] 2 (iPr) Cl and 2 (Ph) I (cbzdiphos=1,8-bis(phosphino)-3,6-di-tert-butyl-9H-carbazole). The arene complexes were also found to be directly accessible from the triiodide [(Cbzdiphos(Ph) )ZrI3 ] through an in situ reaction with a dibenzylmagnesium reagent and subsequent hydrogenolysis, as exemplified for the η(6) -mesitylene complex [(Cbzdiphos(Ph) )Zr(η(6) -mes)I] (3 (Ph) I). The tolyl-ring in 2 (iPr) Cl adopts a puckered arrangement (fold angle 23.3°) indicating significant arene-1,4-diido character. Deuterium labeling experiments were consistent with an intramolecular reaction sequence after the initial hydrogenolysis of a Zr-C bond by a σ-bond metathesis. A DFT study of the reaction sequence indicates that hydrogenolysis by σ-bond metathesis first occurs at the cyclometalated ancillary ligand giving a hydrido-benzyl intermediate, which subsequently reductively eliminates toluene that then coordinates to the Zr atom as the reduced arene ligand. Complex 2 (Ph) I was reacted with 2,6-diisopropylphenyl isocyanide giving the deep blue, diamagnetic Zr(II) -diisocyanide complex [(Cbzdiphos(Ph) )Zr(CNDipp)2 I] (4 (Ph) I). DFT modeling of 4 (Ph) I demonstrated that the HOMO of the complex is primarily located as a "lone pair on zirconium", with some degree of back-bonding into the C≡N π* bond, and the complex is thus most appropriately described as a zirconium(II) species. Reaction of 2 (Ph) I with trimethylsilylazide (N3 TMS) and 2 (iPr) Cl with 1-azidoadamantane (N3 Ad) resulted in the formation of the imido complexes [(Cbzdiphos(R) )Zr=NR'(X)] 5 (iPr) Cl-NAd and 5 (Ph) I-NTMS, respectively. Reaction of 2 (iPr) Cl with azobenzene led to N-N bond scission giving 6 (iPr) Cl, in which one of the NPh-fragments is coupled with the carbazole nitrogen to form a central η(2) -bonded hydrazide(-1), whereas the other NPh-fragment binds to zirconium acting as an imido-ligand. Finally, addition of pyridine to 2 (iPr) Cl yielded the dark purple complex [(Cbzdiphos(iPr) )Zr(bpy)Cl] (7 (iPr) Cl) through a combination of CH-activation and C-C-coupling. The structural data and UV/Vis spectroscopic properties of 7 (iPr) Cl indicate that the bpy (bipyridine) may be regarded as a (dianionic) diamido-type ligand.

Reaction of the precursor complex [RuHCl(CO)(PPh 3 ) 3 ] with the PNP

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The N-perfluoro-phenylated pyridyldiamine H2N2(PFP)N(py) (1) has been prepared by a palladium-catalyzed coupling of hexafluorobenzene and the diamine (H2NCH2)2C(CH3)(2-C5H4N) using the palladacycle trans-di(μ-acetato)bis[o-(di-o-tolylphosphino)benzyl]palladium(II) as catalyst. Reactions of H2N2(PFP)N(py) and Zr(NMe2)4 at room temperature or 90 °C led to the complexes [(N(PFP)N2(TFAP)N(py))ZrF(NMe2)] (2) and [(N2(TFAP)N(py))ZrF2] (3) in which one or two dimethylamido groups replaced one or two ortho fluorine atoms of the pentafluorophenyl groups in the ligand. Reaction of Me3SiX (X = Cl, I) with [(N2(TFAP)N(py))ZrF2] (3) resulted in the formation of mixed halogenated complexes [(N2(TFAP)N(py))ZrFI] (4) and [(N2(TFAP)N(py))ZrFCl] (5) in which the axially bound fluorido ligand is substituted. Reaction of [(N2(TFAP)N(py))ZrF2] (3) with LiNHNPh2 afforded the monohydrazido(1-) complex [(N2(TFAP)N(py))ZrF(NHNPh2)] (6) which was converted to the dimeric fluoro-potassium bridged hydrazinediido complex [Zr(N2(TFAP)N(py))FNNPh2K]2 (7) using KHMDS. The corresponding reaction with LiHMDS yielded the monomeric, donor free complex [Zr(N2(TFAP)N(py))NNPh2] (8).