η⁶-Arene-Zirconium-PNP-Pincer Complexes: Mechanism of Their Hydrogenolytic Formation and Their Reactivity as Zirconium(II) Synthons

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Synthesis and Reactivity of Group 4 Metal Benzyl Complexes Supported by Carbazolide-Based PNP Pincer Ligands

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

[2 + 2] Cycloaddition Products of Zirconium and Hafnium Hydrazinediides with Allenes and Heteroallenes and Their Thermally Induced Rearrangements

Reactions of the hydrazinediido complexes [M­(N₂^TBSN_py)­(NNPh₂)­(py)] (M = Zr (<b>1a</b>), Hf (<b>1b</b>)) with (hetero)­allenes result in a variety of [2 + 2] cycloaddition products of the general type [M­(N₂^TBSN_py)­(κ²<i>N,E</i>-(E­(E′R)­NNPh₂)­(py)] (E = CH₂, S; E′ = CH, N; R = alkyl, aryl). The reaction of [Zr­(N₂^TBSN_py)­(NNPh₂)­(py)] (<b>1a</b>) with 1 molar equiv of phenyl or mesityl isothiocyanate at room temperature yields [Zr­(N₂^TBSN_py)­(κ²<i>N,S</i>-SC­(NAr)­NNPh₂)­(py)] (Ar = phenyl (<b>2a</b>), mesityl (<b>2b</b>)). Reacting the hydrazinediides [M­(N₂^TBSN_py)­(NNPh₂)­(py)] (M = Zr (<b>1a</b>), Hf (<b>1b</b>)) with allenes results in the formation of the metallaazacyclobutanes [M­(N₂^TBSN_py)­(κ²<i>N</i>,<i>C</i>-N­(NPh₂)­CH₂CCH­(R))­(py)] (M = Zr, R = Ph (<b>4a</b>), cyclohexyl (<b>5a</b>), methyl (<b>6</b>); M = Hf, R = phenyl (<b>4b</b>), cyclohexyl (<b>5b</b>)). Subsequent heating of the cycloaddition products revealed different reactivity patterns: the complex [Zr­(N₂^TBSN_py)­(κ²<i>N,S</i>-SC­(NAr)­NNPh₂)­(py)] (<b>2a</b>) forms the isomerization product [Zr­(N₂^TBSN_py)­(κ²<i>N,S-</i>SC­(NNPh₂))­NPh] (<b>3</b>), retaining the N–N bond of the hydrazide. In contrast, the metallacyclobutanes <b>4a</b>,<b>b</b> and <b>5a</b>,<b>b</b> show a tendency toward N–N bond cleavage, resulting in the formation of the C–N- and C–C-coupled product complexes [M­(κ⁴<i>N,N,N,N</i>-N₂^TBSN_pyNC­(Me)CHCy)­(NPh₂)] (M = Zr (<b>7a</b>), Hf (<b>7b</b>)), [Zr­(N₂^TBSN_py)­(κ²<i>N</i><i>,C-</i>(Ph)­NC₆H₄C­(Me)C­(Ph)­NH)] (<b>8</b>) and [Zr­(κ⁴<i>N,N,N,N</i>-N₂^TBSN_pyNC­(Me)=CHPh)­(NPh₂)] (<b>9</b>)

Zirconium Complexes Supported by an <i>N-</i>Perfluoro-Arylated Diamidopyridyl Ligand: Synthesis of Hydrazinediido Complexes

The <i>N-</i>perfluoro-phenylated pyridyldiamine H₂N₂^PFPN_py (<b>1</b>) has been prepared by a palladium-catalyzed coupling of hexafluorobenzene and the diamine (H₂NCH₂)₂C­(CH₃)­(2-C₅H₄N) using the palladacycle <i>trans</i>-di­(μ-acetato)­bis­[<i>o</i>-(di-<i>o</i>-tolylphosphino)­benzyl]­palladium­(II) as catalyst. Reactions of H₂N₂^PFPN_py and Zr­(NMe₂)₄ at room temperature or 90 °C led to the complexes [(N^PFPN₂^TFAPN_py)­ZrF­(NMe₂)] (<b>2</b>) and [(N₂^TFAPN_py)­ZrF₂] (<b>3</b>) 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^TFAPN_py)­ZrF₂] (<b>3</b>) resulted in the formation of mixed halogenated complexes [(N₂^TFAPN_py)­ZrFI] (<b>4</b>) and [(N₂^TFAPN_py)­ZrFCl] (<b>5</b>) in which the axially bound fluorido ligand is substituted. Reaction of [(N₂^TFAPN_py)­ZrF₂] (<b>3</b>) with LiNHNPh₂ afforded the monohydrazido(1−) complex [(N₂^TFAPN_py)­ZrF­(NHNPh₂)] (<b>6</b>) which was converted to the dimeric fluoro-potassium bridged hydrazinediido complex [Zr­(N₂^TFAPN_py)­FNNPh₂K]₂ (<b>7</b>) using KHMDS. The corresponding reaction with LiHMDS yielded the monomeric, donor free complex [Zr­(N₂^TFAPN_py)­NNPh₂] (<b>8</b>)

Borane-Bridged Ruthenium Complex Bearing a PNP Ligand: Synthesis and Structural Characterization

Reaction of the precursor complex [RuHCl­(CO)­(PPh₃)₃] with the PNP protioligand CbzdiphosH in toluene resulted in the formation of two stereoisomeric hydrido complexes, [(CbzdiphosH)­RuHCl­(CO)] (<b>A</b>). The addition of a strong base (KO^tBu or LiEt₃BH), on the other hand, led to the formation of the 1,2-dehydrochlorination product [(Cbzdiphos)­RuH­(CO)]. The reaction of the latter with BH₃·THF at room temperature led to the 1,2-addition of the BH₃ moiety to the Ru–N function, forming a RuNBH cycle in [(CbzdiphosHBH₂)­RuH­(CO)] (<b>B</b>). The same borane-bridged compound was obtained when complex <b>A</b> was treated with NaBH₄ in THF. The BH₂ group forms a bridging unit between the carbazole-N atom and one of the ruthenium-bound hydrides