The reaction of 1,2‐dipiperidinoacetylene (1) with 0.5 equivalents of SnCl2 or GeCl2⋅dioxane afforded the 1,2,3,4‐tetrapiperidino‐1,3‐cyclobutadiene tin and germanium dichloride complexes 2 a and 2 ...b, respectively. A competing redox reaction was observed with excess amounts of SnCl2, which produced a tetrapiperidinocyclobutadiene dication with two trichlorostannate(II) counterions. Heating neat 1 to 110 °C for 16 h cleanly produced the dimer 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne (3); its reaction with stoichiometric amounts of SnCl2 or GeCl2⋅dioxane furnished the 1,3,4,4‐tetrapiperidino‐1,2‐cyclobutadiene tin and germanium dichloride complexes 4 a and 4 b, respectively. Transition‐metal complexes containing this novel four‐membered cyclic bent allene (CBA) ligand were prepared by reaction of 3 with (tht)AuCl, RhCl(CO)22, and (Me3N)W(CO)5 to form (CBA)AuCl (5), (CBA)RhCl(CO)2 (6), and (CBA)W(CO)5 (7). The molecular structures of all compounds 2–7 were determined by X‐ray diffraction analyses, and density functional theory (DFT) calculations were carried out to rationalise the formation of 3 and 4 a.
Cyclic bent allenes as ligands: The thermal dimerisation of 1,2‐dipiperidinoacetylene affords 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne, which provides access to main‐group and transition‐metal complexes of a strongly electron‐donating four‐membered cyclic bent allene ligand. The formation of these complexes as well as the dimerisation of 1,2‐dipiperidinoacetylene were also studied by computational methods.
This paper focuses on the stable, ferrocene-based N-heterocyclic carbene (NHC) rac-Fe{(η5-t-BuC5H3)NpN}2C: (A′-Np, Np = neopentyl), which is planar-chiral due to the two tert-butyl substituents in ...3,3′-positions. A′-Np was synthesized in nine steps starting from 1,1′-di-tert-butylferrocene (1), the first step being its 3,3′-dilithiation to afford rac-Fe(η5-t-BuC5H3Li)2 (rac-fc′Li2, 2). The structures of rac-fc′(SiMe3)2 (3), rac-fc′Br2 (4), rac-fc′(N3)2 (5), and the immediate carbene precursor A′-NpHBF4 were determined by single-crystal X-ray diffraction (XRD). The chemical properties of A′-Np were found to be very similar to those of its tert-butyl-free congener A-Np, both being ambiphilic NHCs with rather high calculated HOMO energies (ca. −4.0 eV) and low singlet–triplet gaps (ca. 35 kcal/mol). A Tolman electronic parameter value of 2050 cm–1 was derived from IR data of cis-RhCl(A′-Np)(CO)2, indicating the high donicity of A′-Np as a ligand. Consistent with its ambiphilic nature, A′-Np was found to react readily with carbon monoxide, affording the betainic enolate (A′-Np)2CO as four stereoisomers, viz. (R p R p-A′-Np)C(O–)(R p R p-A′-Np +), (S p S p-A′-Np)C(O–)(S p S p-A′-Np +), (R p R p-A′-Np)C(O–)(S p S p-A′-Np +), and (S p S p-A′-Np)C(O–)(R p R p-A′-Np +). The former two isomers were structurally characterized as a racemic compound by single-crystal XRD. A′-Np was found to react swiftly with dichloromethane, affording the addition product A′-NpH–CHCl2 in a reaction that is unprecedented for diaminocarbenes. A-NpH–CHCl2 was obtained analogously. Both compounds were structurally characterized by single-crystal XRD. An electrochemical investigation of A′-Np by cyclic and square wave voltammetry revealed a reversible oxidation of the carbene at a half-wave potential of −0.310 vs ferrocene/ferrocenium (THF/NBu4PF6). The electrochemical data previously published for A-Np were identified to be incorrect, since unnoticed hydrolysis of the NHC had taken place, affording A-Np(H2O). The hydrolysis products of A-Np and A′-Np were found to be reversibly oxidized at half-wave potentials of −0.418 and −0.437 V, respectively.
The reactivity of the diaminoacetylene Pip‐C≡C‐Pip (Pip=piperidyl=NC5H10) towards phenyldichloro‐ and triphenylborane is presented. In the case of the less Lewis acidic PhBCl2, the first example of a ...double Lewis adduct of a vicinal dicarbenoid is reported. For the more Lewis acidic triphenylborane, coordination to the bifunctional carbene leads to a mild B−C bond activation, resulting in a syn‐1,2‐carboboration. Ensuing cis/trans isomerization yields a novel ethylene‐bridged frustrated Lewis pair (FLP). The compounds were characterized using multinuclear NMR spectroscopy, structural analysis, and mass spectrometry. Reactivity studies of both isomers with the N‐heterocyclic carbene 1,3‐dimethylimidazol‐2‐ylidene (IMe) aided in elucidating the proposed isomerization pathway. DFT calculations were carried out to elucidate the reaction mechanism. The rather low free energy of activation is consistent with the observation that the reaction proceeds smoothly at room temperature.
More than the sum of its parts: The reactivity of a vicinal dicarbenoid towards organoboron reagents has been investigated. Depending on the Lewis acidity of the borane, double adduct formation or B−C bond activation in a formal syn‐1,2‐carboboration is observed. The obtained activation product undergoes cis/trans isomerization to an internal Lewis pair.
Efficient and simple methods for the large-scale preparation of 1,1′-ferrocenedicarboxylic acid, fc(COOH)2, involving the sodium salts of cyclopentadienecarboxylic methyl and ethyl esters, ...Na(C5H4COOR) (R = Me, Et), are presented. With fc(COOH)2 at hand, the syntheses of various 1,1′-disubstituted compounds of the type fcX2 (X = CH2OH, COCl, CON3, NCO, NHCOOMe, NHBoc, NH2) were optimized and scaled up. The X-ray crystal structures of fc(COOEt)2, fc(NCO)2·1/2C6H6, and fc(NHCOOMe)2·MeOH are reported.
Treatment of Ln(CH2SiMe3)3(thf)2 (Ln = Sc, Y, and Lu) with 1 equiv of CpPN-type ligands C5H4PPh2–NH–C6H3R2 (R = Me, L1(Me); R = i Pr, L1( i Pr)) at room temperature readily generated the ...corresponding CpPN-type bis(alkyl) complexes 1 and 2a–2c. Addition of 3 equiv of LiCH2SiMe3 to a mixture of L1( i Pr) and LnCl3(thf)2 (Ln = Sm and Nd) also afforded the CpPN-type bis(alkyl) complexes 2d and 2e. The Cp moiety bonds to the central metal in a classical η5 mode in all CpPN-type complexes 1 and 2. In contrast, the CpMePN-type ligands C5Me4H–PPh2N–C6H3R2 (R = Me, L2(Me); R = i Pr, L2( i Pr)) behaved differently. L2(Me) did not react with Sc(CH2SiMe3)3(thf)2. Similarly, L2( i Pr) was also inert to Sc(CH2SiMe3)3(thf)2 even at 50 °C. When the central metal was changed to yttrium, however, the equimolar reaction between Y(CH2SiMe3)3(thf)2 and L2( i Pr) in the presence of LiCl afforded two bis(alkyl) complexes 3a and 3b. In the main product 3a, C5HMe3(η3-CH2)–PPh2N–C6H3 i Pr2Y(CH2SiMe3)2(thf), the ligand bonds to the Y3+ ion in a rare η3-allyl/κ-N mode, whereas in 3b, (C5Me4–PPh2N–C6H3 i Pr2)Y(CH2SiMe3)2(LiCl)(thf), the Cp ring coordinates to the Y3+ ion in an η5 mode, and a LiCl unit is located between the Y3+ ion and the nitrogen atom. When the central metal was changed to lutetium, a bis(alkyl) complex 4a, C5HMe3(η3-CH2)–PPh2N–C6H3 i Pr2Lu(CH2SiMe3)2(thf), and a bis(alkyl) complex 4b, (C5Me4–PPh2N–C6H3 i Pr2)Lu(CH2SiMe3)2, were isolated. The protonolysis reaction of the IndPN-type ligands C9H7–PPh2N–C6H3R2 (R = Me, L3(Me); R = Et, L3(Et); R = i Pr, L3( i Pr)) with Ln(CH2SiMe3)3(thf)2 (Ln = Sc, Y, and Lu) generated the IndPN-type bis(alkyl) complexes 5a–5c, 6, and 7a–7c, selectively, where the Ind moiety tends to adopt an η3-bonding fashion. The more bulky FluPN-type ligands C13H9–PPh2N–C6H4R (R = H, L4(H); R = Me, L4(Me)) were treated with Ln(CH2SiMe3)3(thf)2 (Ln = Sc and Lu) to afford the FluPN-type bis(alkyl) complexes 8 and 9a and 9b, where the Flu moiety has a rare η1-bonding mode. Complexes 1–9 were fully characterized by 1H, 13C, and 31P NMR; X-ray; and elemental analyses. Upon activation with AlR3 and Ph3CB(C6F5)4, the scandium complexes showed good to high catalytic activity for ethylene polymerization. The effects of the sterics and electronics of the ligand, the loading and the type of AlR3, the polymerization temperature, and the polymerization time on the catalytic activity were also discussed.
The reaction of dipiperidinoacetylene (pipCCpip, pip = NC5H10, 1a) with Cp2Ti(η2-btmsa) (2) or with Cp2Zr(η2-btmsa)(py) (4) (btmsa = bis(trimethylsilyl)acetylene, py = pyridine) afforded the ...metallacyclopentadienes Cp2M(C4pip4) (3, M = Ti; 5, M = Zr), which in the solid state exhibit twisted five-membered metallacycles with an unusual half-chair conformation. In contrast, the sterically more demanding decamethyltitanocene (Cp*2Ti) and -zirconocene (Cp*2Zr) complex fragments can only accommodate one alkyne ligand. Thus, the titanacyclopropene Cp*2Ti(C2pip2) (7) was isolated from the reaction of 1a with Cp*2Ti(η2-btmsa) (6) or with Cp*2TiCl in the presence of magnesium, whereas the zirconacyclopropenes Cp*2Zr(C2X2) (8a, X = pip; 8b, X = NC5H9-4-Me; 8c, X = NEt2) were prepared by the reduction of Cp*2ZrCl2 with magnesium in the presence of 1a, bis(4-methylpiperidino)acetylene (1b), and bis(diethylamino)acetylene (1c), respectively. NMR studies showed that complexes 8 are in equilibrium with their tucked-in tetramethylpentafulvene–diaminovinyl isomers Cp*(η6-C5Me4CH2)Zr(CX=CHX) (9) in solution, which are formed by intramolecular C–H-bond activation and hydrogen transfer from one Cp* methyl group to the alkyne ligand. Thermodynamic and kinetic parameters were derived by variable-temperature NMR spectroscopy and DFT experiments. The molecular structures of 3, 5, 7, 8a, 8a·MgCl22, 8b, and 8c were established by X-ray diffraction analyses.
Electron‐rich diaminoalkynes with a variable substitution pattern can be conveniently prepared by lithiation of 2,2‐dibromo‐1,1‐ethenediamines; the alkynes are formed by a Fritsch–Buttenberg–Wiechell ...rearrangement of intermediate LiBr–vinylidene species. The first two X‐ray crystal structures of diaminoalkynes are presented, which show almost perpendicular orientations of the NC3 planes.
The Staudinger reaction of organic azides tBuN3, 1‐Ad‐N3, and DippN3 (Dipp = 2,6‐diisopropylphenyl) with (R)‐N,N′‐bis(diphenylphosphanyl)‐2,2′‐diamino‐1,1′‐binaphthyl (R)‐Binam‐P, obtained by an ...optimized procedure from (R)‐(+)‐Binam, Ph2PCl, and Et3N in DCM, leads to preparation of a series of new C2‐symmetric bis‐iminophosphonamide ligands (R)‐Binam(Ph2PN(H)R)2 R = tBu (1), Ad (2), and Dipp (3). The molecular structure of 1·2DMSO was confirmed by X‐ray structure analysis.
A convenient one‐pot synthetic protocol towards THF and DME solvates of lanthanum and other early lanthanide tribromides was developed using the water‐catalyzed reaction of lanthanide(III) oxides ...with highly reactive Me3SiBr in situ formed from commercially available disilane Si2Me6 and Br2. This practical route allows to obtain the target lanthanum tribromide solvates LaBr3(thf)4 (1a) and LaBr3(dme)22 (1b) as well as analogous early lanthanide molecular tribromide solvates NdBr3(thf)4 (2a), NdBr3(dme)2 (2b), SmBr3(thf)2 (3a), and SmBr3(dme)2 (3b) difficult to prepare by other solution‐based procedures. The molecular structure of 1b·2CH2Cl2 was determined by an XRD study.
The Staudinger reaction of organic azides
t
BuN
3
, 1‐Ad‐N
3
, and DippN
3
(Dipp = 2,6‐diisopropylphenyl) with (
R
)‐
N
,
N
′‐
bis
(diphenylphosphanyl)‐2,2′‐diamino‐1,1′‐binaphthyl (
R
)‐Binam‐P, ...obtained by an optimized procedure from (
R
)‐(+)‐Binam, Ph
2
PCl, and Et
3
N in DCM, leads to preparation of a series of new
C
2
‐symmetric bis‐iminophosphonamide ligands (
R
)‐Binam(Ph
2
PN(H)R)
2
R =
t
Bu (
1
), Ad (
2
), and Dipp (
3
). The molecular structure of
1·
2DMSO was confirmed by X‐ray structure analysis.
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