D. A. Lemenovskii

Zr and Hf metallocenes. Study of the structure of a novel mononuclear zirconium trivalent organometallic

Cp2∗MCl2, M  Zr and Hf, were obtained by reaction of MCl4 with Cp∗Li, where Cp∗  1,3-di-tertbutylcyclopentadienyl. Reduction of Cp2∗MCl2 with metallic potassium in pentane gave Cp2∗MCl. The molecular and crystal structure of Cp2∗ZrCl was established from X-ray diffraction; monoclinic, space group P21/b, a  12.722, b  16.336, c  13.426 A, γ  70.68°, R  0.065; monomeric Cp2∗ZrCl molecules, the average ZrC bond length is 2.505 A, that of ZrCl is 2.423 A, and the Cp∗centroidZrCp∗centroid angle is 133.3°.

NIOBOCENE SILYL HYDRIDE COMPLEXES WITH NONCLASSICAL INTERLIGAND HYPERVALENT INTERACTIONS

Niobocene mono- and bis(silyl) hydrides with dimethylhalosilyl groups exhibit a nonclassical interligand hypervalent interaction (IHI) between the hydride and silyl ligands. These interactions result in well-defined structural and reactivity trends and were found in two forms: three-centre, four-electron (A) and five-centre, six-electron (B), as shown schematically.

Diamagnetic and paramagnetic binuclear cyclopentadienyl-fulvalene-nitrene complexes of niobium: Synthesis, spectra and structure

Abstract Oxidation of the diamagnetic binuclear niobium complexes (η 5 :η 5 -C 5 H 4 C 5 H 4 )-(C 5 H 5 ) 2 Nb 2 (μ-NC 6 H 4 R) 2 (R = H and OCH 3 ) (I) yields stable paramagnetic cations [η 5 :η 5 -C 5 H 4 C 5 H 4 C 5 H 4 ) (C 5 H 5 ) 2 Nb 2 (η-NC 6 H 4 R) 2 ] + (II). IR, EPR, and UV spectra of I and II have been studied. The crystal and molecular structures of I and II with R = OCH 3 have been determined and compared.

Alkyl(amino)- and Alkyl(chloro)phosphanyl-Substituted Cyclopentadienyl Complexes of Titanium and Zirconium

Phosphanyl-substituted cyclopentadienes of the type [RnCp−PR(NR1R2/Cl)] (1−22) (R = Alk, Ar; R1, R2 = H, Alk, Ar, SiR3; RnCp = tBuCp, Me4Cp, Ind, Me6Ind, Flu) can be synthesised by reaction of alkyldichlorophosphanes and alkyl(amino)chlorophosphanes with alkali metal cyclopentadienides. The method used is a general one and provides high isolated yields of the target compounds. The phosphanylcyclopentadienes can easily be deprotonated by strong bases (e.g. nBuLi, PhCH2K, Ph2CHK) and the potassium salts [RnCp−PR(NR1R2)]K (25−28) are efficiently transmetallated by Me3SnCl. A subsequent reaction with TiCl4(L)2 and ZrCl4(L)2 (L = THF, tetrahydrothiophene, Me3P) affords new half-sandwich complexes [{Me4Cp−PtBu(NEt2)}TiCl3] (36), [{Me4Cp−PtBu(NEt2)}TiCl3] (37) and [{tBuCp−PtBu(NEt2)}TiCl3] (38) in moderate yields. The reaction of [tBuCp−PtBu(Cl)] (6) with TiCl4 in the presence of Et3N at low temperature yields the half-sandwich complex [{tBuCp−PtBu(Cl)}TiCl3] (39) quantitatively; [(Cp−PtBu(Cl)]2CMe2] (11) reacts similarly and gives, dependent on the reagent ratio, either the homobimetallic derivative [{(Cp−PtBu(Cl)2CMe2}{TiCl3}2] (40) (1:2 ratio) or the ansa complex [{(Cp−PtBu(Cl)]2CMe2}TiCl2] (41) (1:1 ratio). The scope of this reaction could not be extended to sterically more demanding cyclopentadienyl derivatives. Treatment of [{tBuCp−PtBu(Cl)}TiCl3] (39) by LiN(H)tBu in the presence of Et3N leads to the formation of the constrained geometry complex [{tBuCp−PtBu(NtBu)}TiCl2] (42) in a high yield. All synthesised compounds were characterised by NMR spectroscopy, mass spectrometry and elemental analyses. The crystal structures of the ligand precursor [Me6Ind−PtBu(NHtBu)] (15) and that of [{Me4Cp−PtBu(NEt2)}TiCl3] (36) have been determined by X-ray diffractometry. The complexes described in this work are active in the MAO-mediated polymerisation of ethylene.

Hetero-ansa-metallocenes: I. Synthesis of the novel [1]-borylidene-bridged ansa-zirconecene dichloride

Abstract The first ansa -[1]-zirconecene dichloride with the boron bridge atom, [( μ −PhB)( η 5 −C 5 H 4 ) 2 ]ZrCl 2 (5) is synthesised via subsequent transmetallation of C 5 H 4 (SnMe 3 ) 2 by PhBCl 2 and ZrCl 4 . The unstable corresponding ligand — PhB(C 5 H 5 ) 2 (1) — was synthesised and isolated in the form of pyridine (1:1) (2) and DABCO (2:1 (3) adducts.

Contrasting Nonclassical Silicon−Hydrogen Interactions in Niobium and Tantalum Half-Sandwich Complexes: Si−H···M Agostic versus M−H···Si−Cl Interligand Hypervalent Interactions

Reaction of [CpM(NAr)(PMe3)2] (M = Nb, Ta; Ar = 2,6-C6H3iPr2) with HSiClMe2 gives two remarkably different nonclassical Si···H···M products depending only on the identity of M; [CpTa(NAr)(H)(SiMe2Cl)(PMe3)] possesses an unusual electron-rich M−H···Si interligand hypervalent interaction while [CpNb{η3-N(Ar)SiMe2−H}Cl(PMe3)] is the first example of a β-agostic silylamine Si−H···M interaction showing a “stretched” Si−H bond.

THE CARBENOID NATURE OF HALOPHOSPHINES. CARBENE-LIKE INSERTION MECHANISM IN THE REACTION OF CHLOROPHOSPHINES WITH CP2NBH3

Abstract We have studied the reactivity of Cp2NbH3 (1) with different chlorophosphines and showed that all the reactions occur at the niobium-hydride bond and proceed by two competitive routes, via the direct insertion of a chlorophosphine into the NbH bond and electron or/and hydride transfer mechanism. Reaction of 1 with the unhindered dialkyl- and diaryl-chlorophosphines CIPR2 (R = Et, Bu, Pr1, Ph) gave the insertion product — the ionic complexes [Cp2NbH2(PHR2)]Cl (2) — in high yields. In contrast, reaction of 1 with the bulkier ClPBu21 proceeded much slower and resulted in the steady formation of Cp2NbCl2 and HPBu21. Cp2NbCl2 was also the product of the reactions of 1 with excess of ClP(OEt)2 and catecholechlorophosphine 7. The reaction of 1 with one equivalent of cyclic chlorodiaminophosphine ClP(N(CH3)2CH2−)2 (5) resulted in two competitive routes that led to the ionic complex [Cp2NbH2(HP(NR2)2)]Cl (2f) and molecular complex Cp2NbCl(HP(NR2)2) (6j). The reaction of 1 with two equivalents of cyclic 1-chloro-5,5-dimethyl-1-phospha-2,6-dioxahexane gave cationic diphosphite complex [Cp2Nb(PHR2)2]Cl (8) in high yield. This reactivity was explained in terms of the carbenoid nature of halophosphines due to the proposed relationship in the electronic structures of halophosphines and singlet methylene. Thus, reaction of 1 with the unhindered dialkyl- and diaryl-chlorophosphines proceeded by the direct insertion of a chlorophosphine ClPR2 into the NbH bond whereas with the more electron withdrawing substituents R at phosphorus the electron or/and hydride transfer mechanisms, leading to 6 and eventually to Cp2NbCl2, could be operative. This concept also allowed us to explain the reactivity of chlorophosphines toward different unsaturated organic products. The facile syntheses of complexes Cp2Nb(PHR2)Cl (6) and Cp2Nb(PHR2)H (11) by the thermolysis and deprotonation of 2, respectively, was performed and the comparison with other methods was undertaken. Crystallographic studies of complexes 8 and Cp2Nb(PHPr21)Br are reported.

Polyelement substituted cyclopentadienes and indenes — Novel ligand precursors for organotransition metal chemistry

Abstract A series of polyelement substituted cyclopentadienyl and indenyl boranes and arsanes containing Me 3 Si-, Me 3 Sn- was synthesised; (C 5 H 4 SiMe 3 )BX 2 ( 2 , X = Cl; 3 , X = Br) and (C 9 H 6 SiMe 3 )BX 2 ( 4 , X = Cl; 5 , X = Br) were obtained by Si/B exchange reaction in a low yield when X = Cl and in a moderate yield when X = Br, whereas Flu(SIMe 3 ) 2 does not react with BBr 3 at all. PhB(C 5 H 4 SiMe 3 ) 2 ( 6 ) and PhB[C 5 H 3 (SiMe 3 ) 2 ] 2 ( 7 ) were synthesised using appropriate thallium cyclopentadienides in high yields, 81% and 99% respectively. More bulky indenyl derivatives TrsB(C 9 H 7 ) 2 ( 8 , Trs = (Me 3 Si) 3 C—), PhB(C 9 H 6 SiMe 3 ) 2 ( 9 ), Ph 2 B(C 9 H 6 SiMe 3 ) ( 10 ) were prepared by metathesis reactions of lithium indenides with boron halides in high yields. A subsequent transmetallation of C 9 H 6 (SnMe 3 ) 2 with PhBCl 2 followed by addition of ZrCl 4 gave (η 5 -C 9 H 6 SnMe 2 Cl) 2 ZrCl 2 ( 11 ) in the form of one of two possible diastereomers in high yield. C 9 H 6 (SiMe 3 )SnMe 3 reacts with BCl 3 to give the appropriate bis-indenyl derivative, that was easily converted to the ansa -zirconocene complex [MeB(η 5 -C 9 H 6 ) 2 ]ZrCl 2 ( 12 ). The sterically demanding bis-indenyl ligand 8 underwent direct deprotonation by t -BuLi, affording [TrsB(η 5 -C 9 H 6 ) 2 ]ZrCl 2 ( 13 ) by in situ reaction with Me 3 SnCl and ZrCl 4 . Indenylarsanes (C 9 H 7 ) 3 As ( 14 ), t -BuAs(C 9 H 7 ) 2 ( 15 ), C 9 H 7 AsMe 2 ( 16 ) and (C 9 H 6 SiMe 3 )AsMe 2 ( 17 ) were synthesised by reactions of lithium indenides with asenic halides in good to excellent yields. All these compounds were characterized by analytical and spectroscopic data (NMR, MS). 14 and 15 exist as complex isomeric mixtures with the arsenic atom in the allylic position of the indenyl ring; the crystal structure of a meso form of 15 was determined by X-ray diffraction methods. 17 consists of two isomers with a vinylic ( 17a ) and an allylic ( 17b ) Me 3 Si substituent. Stannylation of 16 by Me 3 SnNEt 2 led exclusively to the diallylic derivative (C 9 H 6 AsMe 2 )SnMe 3 ( 18 ) in quantitative yield. The latter was readily converted to a polymeric, half-sandwich indenyl zirconocene [η 5 -(C 9 H 6 AsMe 2 )ZrCI 3 ] n ( 19 ) in high yield. Further reaction of 19 with Cp * Li resulted in the formation of a new arsano substituted bent metallocene complex [η 5 -(C 9 H 6 AsMe 2 )-η 5 -(C 5 Me 5 )]ZrCl 2 ( 20 ) in good yield.

The first bismuthido-substituted niobocene

Abstract The reaction of Cp2NbH3 with ClBiPh2 in THF in the presence of amine resulted in the formation of the first bismuthido-substituted niobocene, Cp2NbH2BiPh2 (1), having a unique combination of an early transition metal, a bismuthido ligand and a hydride ligand. This highly unstable compound was characterized by 1H and 13C NMR spectroscopy. One of the decomposition pathways for 1 was found to proceed via breaking of the BiPh bond.

New metallocene complexes of Nb and Ta with functionalized diazoalkanes

The reaction of Cp2MH3, where M  Nb or Ta, with N2CPh2, N2CPh(o-C6H4Br) and N2CHCOOEt was thoroughly studied. It was shown that the primary products of the reaction are the complexes Cp2M(H)(η1-N2CRR′) (2). The complexes 2 are readily oxidized by air to give polymeric (Cp2MO)n, N2CRR′ and RR′CN2CRR′. Interaction of an excess of N2CPh(o-C6H4Br) with Cp2NbH3 leads to a 17-electron complex Cp2Nb( NNCPho-C6H4)2 (6) with two σ-N pyrazole ligands. Finally the reaction of Cp2NbH3 with N2CHCOOEt gives an unusual dimeric complex Cp2Nb2(η5-C5H4C(COOEt)N μ-N)2. The complexes 2 were found to undergo easily substitution of a hydride ligand for a halogen atom. The results of X-ray analysis of the complexes 6 and Cp2Nb(Cl)-η1-N2CPh(o-C6H4Br) are provided.