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1.
Dalton Trans ; 41(8): 2277-88, 2012 Feb 28.
Article in English | MEDLINE | ID: mdl-22223159

ABSTRACT

We report a combined experimental and computational comparative study of the reactions of the homologous titanium dialkyl- and diphenylhydrazido and imido compounds Cp*Ti{MeC(N(i)Pr)(2)}(NNR(2)) (R = Me (1) or Ph (2)) and Cp*Ti{MeC(N(i)Pr)(2)}(NTol) (3) with silanes, halosilanes, alkyl halides and [Et(3)NH][BPh(4)]. Compound 1 underwent reversible Si-H 1,2-addition to Ti=N(α) with RSiH(3) (experimental ΔH ca. -17 kcal mol(-1)), and irreversible addition with PhSiH(2)X (X = Cl, Br). DFT found that the reaction products and certain intermediates were stabilised by ß-NMe(2) coordination to titanium. The Ti-D bond in Cp*Ti{MeC(N(i)Pr)(2)}(D){N(NMe(2))SiD(2)Ph} underwent σ-bond metathesis with BuSiH(3) and H(2). Compound 1 reacted with RR'SiCl(2) at N(α) to transfer both Cl atoms to Ti; 2 underwent a similar reaction. Compound 3 did not react with RSiH(3) or alkyl halides but formed unstable Ti=N(α) 1,2-addition or N(α) protonation products with PhSiH(2)X or [Et(3)NH][BPh(4)]. Compound 1 underwent exclusive alkylation at N(ß) with RCH(2)X (R = H, Me or Ph; X = Br or I) whereas protonation using [Et(3)NH][BPh(4)] occurred at N(α). DFT studies found that in all cases electrophile addition to N(α) (with or without NMe(2) chelation) was thermodynamically favoured compared to addition to N(ß).


Subject(s)
Nitrogen/chemistry , Protons , Silanes/chemistry , Silicon/chemistry , Titanium/chemistry , Alkylation , Binding Sites , Indicators and Reagents/chemistry , Ligands , Quantum Theory , Substrate Specificity
2.
Chemistry ; 17(1): 265-85, 2011 Jan 03.
Article in English | MEDLINE | ID: mdl-21207623

ABSTRACT

We report a range of new transformations of the diamide-amine supported Ti=NNPh(2) functional group with a variety of unsaturated substrates, along with DFT studies of the key mechanisms. Reaction of [Ti(N(2) N(py) )(NNPh(2) )(py)] (4, N(2) N(py) =(2-NC(5) H(4) )CMe(CH(2) NSiMe(3) )(2) ; py=pyridine) with MeCN gave the dimeric species [Ti(2) (N(2) N(py) )(2) {µ-NC(Me)(NNPh(2) )}(2) ] through a [2+2] cycloaddition process. Reaction of 4 or [Ti(N(2) N(Me) )(NNPh(2) )(py)] (5, N(2) N(Me) =MeN(CH(2) CH(2) NSiMe(3) )(2) ) with fluorinated benzonitriles gave the terminal hydrazonamide complexes [Ti(N(2) N(R) ){NC(Ar F x)NNPh(2) }(py)] (R=py or Me; Ar F x=2,6-C(6) H(3) F(2) or C(6) F(5) ). DFT studies showed that this proceeds through an overall [2+2] cycloaddition-reverse cycloaddition, resulting in net insertion of Ar F xCN into the Ti=N(α) bonds of the respective hydrazides. Reaction of 4 with a mixture of MeCN and PhCCMe gave the metallacycle [Ti(N(2) N(py) ){NC(Me)C(Ph)C(Me)NNPh(2) }] by sequential coupling of Ti=NNPh(2) with PhCCMe and then MeCN. A related product, [Ti(N(2) N(py) ){NC(Me)C(Ar(F) )C(H)NNPh(2) }], was formed by insertion of MeCN into the Ti-C bond of the isolated azatitanacyclobutene [Ti(N(2) N(py) ){N(NPh(2) )C(H)C(Ar(F) )}] (Ar(F) =3-C(6) H(4) F). Reaction of 4 with two equivalents of B(Ar F 5)(3) (Ar F 5=C(6) F(5) ) formed the zwitterionic borate [Ti(N(2) N(py) ){η(2) -N(NPh(2) )B(Ar F 5)(3) }] by electrophilic attack at N(α) . Compounds 4 and 5 reacted with tBuNC and/or XylNC (Xyl=2,6-C(6) H(3) Me(2) ) to give the N(α)-N(ß) bond cleavage products, [Ti(N(2) N(R) )(NCNR')(NPh(2) )] (R=py or Me; R'=tBu or Xyl), containing metallated carbodiimide ligands. DFT studies of these reactions found an initial addition of RNC across Ti=N(α) followed by N(ß) coordination, and finally complete N(α) transfer from the NNPh(2) to the RNC fragment. Reaction of 5 with Ar'NCE (E=O, S, Se; Ar'=2,6-C(6) H(3) iPr(2) ) gave the [2+2] cycloaddition products [Ti(N(2) N(Me) ){N(NPh(2) )C(NAr')O}(py)] and [Ti(N(2) N(Me) ){N(NPh(2) )C(NAr')E}] (E=S or Se), which did not undergo further transformation of the Ti-N-NPh(2) moiety.

3.
J Am Chem Soc ; 132(30): 10484-97, 2010 Aug 04.
Article in English | MEDLINE | ID: mdl-20617837

ABSTRACT

A combined experimental and DFT study of the reactions of diamide-amine supported titanium hydrazides with alkynes is presented. Reaction of Ti(N2N(py))(NNPh2)(py) (1, N2N(py) = (2-NC5H4)CMe(CH2NSiMe3)2) with terminal and internal aryl alkynes ArCCR (Ar = Ph or substituted phenyl, R = Me or H) at room temperature gave the fully authenticated azatitanacyclobutenes Ti(N2N(py)){N(NPh2)C(R)CAr} via ArCCR [2 + 2] cycloaddition to the Ti=N(alpha) bond of the hydrazide ligand. In contrast, reaction of 1 with PhCCMe at 60 degrees C, or of Ti(N2NMe)(NNPh2)(py) (11, N2NMe = MeN(CH2CH2NSiMe3)2) with RCCMe (R = Me, Ph or substituted phenyl) at room temperature or below, gave vinyl imido compounds of the type Ti(N2N(R')){NC(R)C(Me)NPh2}(py), in which RCCMe had undergone net insertion into the N(alpha)-N(beta) bond. These are the first examples of this type of reaction for any metal hydrazide. The reaction of 11 with PhCCMe had the activation parameters DeltaH(double dagger) = 18.8(4) kcal mol(-1), DeltaS(double dagger) = 1(1) cal mol(-1) K(-1) and DeltaG(298)(double dagger) = 18.5(7) kcal mol(-1). Mechanistic and DFT studies for 1 and 11 found that the N(alpha)-N(beta) insertion event is preceded by alkyne cycloaddition to Ti=N(alpha), and that N(alpha)-N(beta) bond "insertion" is really an intramolecular N(alpha) atom migration process within the azatitanacyclobutenes following intramolecular chelation of NPh2 of the hydrazide ligand. Electron-withdrawing aryl groups on ArCCMe stabilize the azatitanacyclobutenes and also promote a specific regiochemistry (ArC carbon bound to Ti). This in turn defines the regiochemistry of the overall N(alpha)-N(beta) insertion reaction (ArC carbon bound to N(alpha)). In contrast, electron-releasing aryl groups promote the final N(alpha) migration stage of the mechanism, and a Hammett analysis of the rates of insertion of (4-C6H4X)CCMe into the N(alpha)-N(beta) bond of 11 found a reaction constant, rho, of -0.74(5), consistent with NPA charge changes of ArC along the DFT reaction coordinate.

4.
Chem Commun (Camb) ; 46(1): 85-7, 2010 Jan 07.
Article in English | MEDLINE | ID: mdl-20024301

ABSTRACT

Nitriles, CO(2) and isocyanates undergo net single or double insertion reactions into the Ti=N(alpha) multiple bonds of terminal titanium hydrazides. These are the first such examples of this type of reactivity for any transition metal hydrazide complex.

5.
Inorg Chem ; 47(24): 12049-62, 2008 Dec 15.
Article in English | MEDLINE | ID: mdl-18998672

ABSTRACT

Reaction of TiCl(2)(Me(2)Calix) with 2 equiv of LiNHNRR' afforded the corresponding terminal hydrazido(2-) complexes Ti(NNRR')(Me(2)Calix) (R = Ph, R' = Ph (1) or Me; R = R' = Me (3)) which were all structurally characterized. The X-ray structure of Ph(2)NNH(2) is reported for comparison. Compound 1 was also prepared from Na(2)[Me(2)Calix] and Ti(NNPh(2))Cl(2)(py)(3). Reaction of ZrCl(2)(Me(2)Calix) with 2 equiv of LiNHNR(2) afforded only the bis(hydrazido(1-)) complexes Zr(NHNR(2))(2)(Me(2)Calix) (R = Ph or Me). Treatment of Ti(NNMe(2))(Me(2)Calix) (3) with MeI gave the zwitterionic hydrazidium species Ti(NNMe(3))(MeCalix) (6) via a net isomerization reaction which was found to be catalytic in MeI. The corresponding reaction of 3 with CD(3)I gave Ti(NNMe(2)CD(3))(MeCalix) (6-d(3)) with concomitant elimination of MeI. Reaction of 3 with 1 equiv of MeOTf gave [Ti(NNMe(3))(Me(2)Calix)][OTf] (7-OTf) which in turn reacted with (n)Bu(4)NI to form 6 and MeI. Addition of PhCHO to 3 gave the mu-oxo dimer [Ti(mu-O)(Me(2)Calix)](2) and benzaldehyde-dimethylhydrazone. Reaction of either 3 or 6 with (t)BuNCO gave the zwitterionic species Ti{(t)BuNC(NNMe(3))O}(MeCalix) (10) which has been crystallographically characterized. Compound 10 is the formal product of insertion of an isocyanate into the Ti=N(alpha) bond of a titanium hydrazide or hydrazidium species (Me(2)Calix or MeCalix = dianion or trianion of the di- or monomethyl ether of p-tert-butyl calix[4]arene, respectively).


Subject(s)
Calixarenes/chemistry , Hydrazines/chemistry , Hydrazines/chemical synthesis , Phenols/chemistry , Crystallization/methods , Hydrazines/metabolism , Hydrogen Bonding , Kinetics , Ligands , Magnetic Resonance Spectroscopy/methods , Models, Molecular , Molecular Conformation , Probability , Spectrophotometry , X-Ray Diffraction
6.
Chem Commun (Camb) ; (41): 5101-3, 2008 Nov 07.
Article in English | MEDLINE | ID: mdl-18956035

ABSTRACT

The first structurally authenticated [2+2] cycloaddition products of any transition metal hydrazide complexes are reported; cycloaddition products of transition metal hydrazides with alkynes and heteroalkynes have been obtained for the first time; these are the first structurally authenticated cycloaddition products for any transition metal M=NNR(2) functional group.


Subject(s)
Alkynes/chemistry , Metals/chemistry , Titanium/chemistry , Transition Elements/chemistry , Azides/chemistry , Cyclization , Models, Molecular , X-Ray Diffraction
7.
Chem Commun (Camb) ; (46): 4937-9, 2007 Dec 14.
Article in English | MEDLINE | ID: mdl-18361375

ABSTRACT

Two broadly applicable strategies for extending the available ligand platforms of the virtually unexplored terminal Ti=N-NR2 functional group are described, along with the highly selective room temperature insertion of alkynes into the N-N bond of Ti{MeN(CH2CH2NSiMe3)2}(NNPh2)(py) and the catalytic cis-diamination of PhC[triple bond]CMe by diphenylhydrazine.


Subject(s)
Alkynes/chemistry , Crystallography, X-Ray , Hydrazines/chemistry , Indicators and Reagents , Ligands , Magnetic Resonance Spectroscopy , Models, Chemical
8.
Chem Commun (Camb) ; (4): 436-8, 2006 Jan 28.
Article in English | MEDLINE | ID: mdl-16493828

ABSTRACT

Ethylene polymerisation productivities of tris(pyrazolyl)methane-supported catalysts [Ti(NR){HC(Me2pz)3}Cl2] show a dramatically different dependence on the imido R-group compared to those of their TACN analogues, attributed to differences in fac-N3 donor topology; when treated with AliBu3, the zwitterionic tris(pyrazolyl)methide compound [Ti(N-2-C6H4tBu){C(Me2pz)3}Cl(THF)] also acts as a highly active, single site catalyst (TACN = 1,4,7-trimethyltriazacyclononane).


Subject(s)
Aza Compounds/chemical synthesis , Imides/chemistry , Organometallic Compounds/chemical synthesis , Pyrazoles/chemical synthesis , Titanium/chemistry , Borates/chemistry , Catalysis , Ligands , Molecular Structure , Polymers/chemistry
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