“…Similar to H 2 CLi 2 , these higly ionic compounds are likely polymeric in the solid state. Recently, some stabilized molecular dilithiomethandiides have been structurally characterized. − The use of the bis(iminophosphorano)methane ligand in the syntheses of a well-defined dilithiomethandiide complex 10 [ 4 − Li 2 ] 2 , as well as in a rather polar lanthanide carbene complex 4 − Sm(NCy 2 )·THF, urged us to probe this ligand in the synthesis of a calcium carbene. …”
Attempted 2-fold deprotonation of the bis(iminophosphorano)methane ligand, H(2)C(Ph(2)P=NSiMe(3))(2) (4-H(2)), with a calcium amide led only to mono-deprotonation. The crystal structure of (4-H)(2)Ca shows two tridentate ligands with short Ca-N and a rather long Ca-C bond. Reaction of 4-H(2) with a dibenzylcalcium complex gave the desired 2-fold deprotonation and formation of 4-Ca, which crystallized as a dimeric complex. Analysis of the calculated atomic and group charges in 4-H(2), (4-H)(2)Ca, and [4-Ca](2) showed that the negative charge at the imine nitrogens only slightly increases upon successive deprotonation of 4-H(2). The electron density at the central carbon, however, increases considerably: the charge on the carbene carbon in [4-Ca](2) is ca. -1.8. The negative charge in 4(2)(-) is therefore mainly located on the carbon. Reaction of [4-Ca](2) with benzophenone in benzene gave the remarkably stable adduct [4-Ca](2) x O=CPh(2), which was characterized by X-ray diffraction. Reaction of [4-Ca](2) with adamantylcyanide gave exclusive formation of the adduct [4-Ca](2) x (N identical withCR)(2), which did not react further, even at higher temperatures. Addition of cyclohexyl isocyanate to a benzene solution of [4-Ca](2) gave immediate [2 + 2]-cycloaddition and formation of a dianionic tetradentate ligand that binds to Ca(2+) through two nitrogens, the central carbon, and an oxygen. This product crystallized as a dimer with bridging oxygen atoms.
“…Similar to H 2 CLi 2 , these higly ionic compounds are likely polymeric in the solid state. Recently, some stabilized molecular dilithiomethandiides have been structurally characterized. − The use of the bis(iminophosphorano)methane ligand in the syntheses of a well-defined dilithiomethandiide complex 10 [ 4 − Li 2 ] 2 , as well as in a rather polar lanthanide carbene complex 4 − Sm(NCy 2 )·THF, urged us to probe this ligand in the synthesis of a calcium carbene. …”
Attempted 2-fold deprotonation of the bis(iminophosphorano)methane ligand, H(2)C(Ph(2)P=NSiMe(3))(2) (4-H(2)), with a calcium amide led only to mono-deprotonation. The crystal structure of (4-H)(2)Ca shows two tridentate ligands with short Ca-N and a rather long Ca-C bond. Reaction of 4-H(2) with a dibenzylcalcium complex gave the desired 2-fold deprotonation and formation of 4-Ca, which crystallized as a dimeric complex. Analysis of the calculated atomic and group charges in 4-H(2), (4-H)(2)Ca, and [4-Ca](2) showed that the negative charge at the imine nitrogens only slightly increases upon successive deprotonation of 4-H(2). The electron density at the central carbon, however, increases considerably: the charge on the carbene carbon in [4-Ca](2) is ca. -1.8. The negative charge in 4(2)(-) is therefore mainly located on the carbon. Reaction of [4-Ca](2) with benzophenone in benzene gave the remarkably stable adduct [4-Ca](2) x O=CPh(2), which was characterized by X-ray diffraction. Reaction of [4-Ca](2) with adamantylcyanide gave exclusive formation of the adduct [4-Ca](2) x (N identical withCR)(2), which did not react further, even at higher temperatures. Addition of cyclohexyl isocyanate to a benzene solution of [4-Ca](2) gave immediate [2 + 2]-cycloaddition and formation of a dianionic tetradentate ligand that binds to Ca(2+) through two nitrogens, the central carbon, and an oxygen. This product crystallized as a dimer with bridging oxygen atoms.
“…Previous studies of lithioalkyl sulfoximines had revealed a 1,3-C,N-coordination of the Li atom as shown in 15a and a low configurational stability of the Cα atom. 8a,b, The later feature is due to a fast 1,3-shift of the Li atom in 15a and 15b and a low barrier for rotation around the Cα−S bond of 20a and 20b . In this respect the lithioalkyl sulfoximine 15 resembles the titanium complex 16 .…”
Section: Resultsmentioning
confidence: 87%
“…The 1,3-C,N-shift of the Li atom of 15 could also take place within a cyclic eight-membered dimer of 15 , the Li atoms of which are each coordinated by a Cα atom and a N atom; see ref a. Alternatively, the topomerization of the hydrogens of the methylene groups could proceed within an ion pair formed through dissoziation of 15 .…”
Variable-temperature (1)H and (13)C NMR spectroscopy of the sulfonimidoyl-substituted allyltitanium(IV) complexes E-1a-c and Z-1a-c, which carry diethylamino groups at the Ti atom, revealed a fast 1,3-C,N-shift of the Ti atom, leading to an equilibrium between the epimeric Calpha-titanium allyl complexes A and C and the N-titanium allyl aminosulfoxonium ylide B. Based on these findings a model for the reactions of E-1a-c and Z-1a-c with aldehydes is proposed, which features regio- and diastereoselective reactions of the N-titanium ylide B at the alpha-position and the Calpha-titanium complex A at the gamma-position. Model ab initio calculations of the methylene and allyl (dimethylamino)sulfoxonium ylides 10 and 14, respectively, revealed short Calpha-S bonds, a stabilization by both electrostatic interaction and negative hyperconjugation, and a low Calpha-S rotational barrier. The ylides preferentially adopt Calpha-S and Calpha-N conformations in which the lone pair orbital at the Calpha atom is periplanar to the S=O bond and that at the N atom periplanar to the Calpha-Ph bond. Variable-temperature NMR spectroscopy of the sulfonimidoyl-substituted alkyltitanium(IV) complex 16, which carries diethylamino groups at the Ti atom, revealed a dynamic behavior leading to a complete topomerization of all four methylene hydrogens of the Calpha-ethyl groups. Two fast processes are held responsible for the topomerization of the hydrogens of 16. The first one is a reversible intramolecular beta-hydride elimination/alkene-Ti-H insertion with the intermediate formation of a complex between (Et(2)N)TiH and a 1-alkenyl sulfoximine, and the second one consists of a reversible 1,3-C,N-shift of the Ti atom in combination with a Calpha-S bond rotation. Interestingly, the room-temperature NMR spectra of the corresponding sulfonimidoyl-substituted alkyltitanium(IV) complex 17, which carries isopropoxy groups at the Ti atom, give no indication of a similar dynamic behavior of this complex.
“…12 Eine ganze Reihe substituierter Derivate wie Me 3 CCHLi 2 , Me 3 SiCHLi 2 13 und die Titelverbindung 9,9‐Dilithiofluoren14 wurden bislang hergestellt, doch sind ihre Strukturen ebenfalls nicht bekannt. Es gelang, von heteroatomsubstituierten Derivaten wie PhS(O)(NMe)CLi 2 Ph,15 (Me 3 SiNPPh 2 ) 2 CLi 2 ,16, 17 (MeO) 2 P(O)CLi 2 SiMe 3 (als Aggregat mit Dimethylamid)18 und PhSO 2 CLi 2 (SiMe 3 )19 Kristallstrukturen zu erhalten, bei denen jedoch Li‐O‐ und Li‐N‐Kontakte strukturdominierend sind. Das Dianion (CHPMe 2 NSiMe 3 ) 2− bildet zusammen mit BuMe 2 SiO − das Gerüst eines Li 14 ‐Clusters 20.…”
Polymere Stränge im Kristall: Der 9,9 ‐ Dilithiofluoren ‐ THF ‐ Komplex (siehe Bild) kristallisiert in Form von Doppelbändern aus Lithiumatomen zwischen denen alternierend Fluorenyliden‐ und THF‐Einheiten verbrücken. Diese Polymerstränge werden durch Li‐C‐π‐ und Li‐C‐σ‐Wechselwirkungen zusammengehalten. Für das tetrametallierte Kohlenstoffatom resultiert die Koordinationszahl sechs. Somit sind hier Strukturelemente vertreten, die einerseits von Lithioalkanen und andererseits etwa vom Lithocenanion her bekannt sind.
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