Structural Variances in the Homologous Series of Di-Alkali-Metalated Octamethylcyclotetrasilazanes

The rubidium and cesium dimetalated derivatives of octamethylcyclotetrasilazane (OMCTS) have been synthesized and crystallographically characterized. This completes the set of di-alkali-metalated OMCTS structures. Comparison of the geometric parameters within the series reveals the cation-induced alterations of coordination and aggregation as well as of bonding within, and conformation of, the anionic fragment. With the increasing size and the decreasing charge-localizing effect of the cation going from lithium to cesium, the coordination number and “haptotropicity” of the cation systematically increases, while the preference of the deprotonated nitrogen atoms over the N(H) functional nitrogen atoms for an electrostatic interaction decreases in this order. At the same time, the distortion of the ring geometry caused by the charge-localizing effect of the cation decreases such that the anionic fragment approaches the symmetric crown conformation. Within the ring system, the character of the Si−N bond becomes more ionic, which explains the increasing deviation of short and long Si−N bond lengths. That properties for a certain species are still not entirely deducible from respective data of homologous compounds is revealed by unexpected inconsistencies within the structural and chemical characteristics of the compounds investigated. For instance, the dimeric aggregation of the potassium compound contrasts with the polymeric form of the rubidium and cesium structures despite the close relationship between these metals. Moreover, the course of reactivity of the elemental alkali metals with respect to the deprotonation of OMCTS seems to conflict with their reduction potentials but can be explained by considering the steric situation at the N(H) active site of the precursor

Syntheses and Structures of [(THF)<i>_n</i>M{(NSiMe₃)₂PPh₂}₂] Complexes (M = Be, Mg, Ca, Sr, Ba; <i>n</i> = 0−2): Deviation of Alkaline Earth Metal Cations from the Plane of an Anionic Ligand^†

The syntheses and solid-state structures of [(THF)nM{(NSiMe3)2PPh2}2] (M = Be, n = 0, 1; M = Mg, n = 0, 2; M = Ca, n = 1, 3; M = Sr, n = 2, 4; M = Ba, n = 2, 5) are presented. Comparison of the geometric parameters within the homologous series and to related systems uncovers the dication-induced alterations of coordination to, as well as bonding within, the anionic fragment. The coordination number increases from 4 (Be, Mg) via 5 (Ca) to 6 (Sr, Ba). Two of the Ph2P(Me3SiN)2 anions cover the coordination sphere of beryllium and magnesium, while with calcium one single THF molecule and with strontium and barium two additional THF molecules are required to complete the metal coordination sphere. Against steric considerations the two THF molecules in 4 and 5 are coordinated to the same hemisphere of the metal leaving the two anions cisoid. Even against sterical strain the alkaline earth metals leave the plane of one of the Ph2P(Me3SiN)2 anions with increasing mass demonstrating the preference of Sr and Ba to interact with π electron density. This effect can also be found in related systems. It might be small and counterbalanced by steric requirements, but it is significant. The metal π interaction rises continually with the mass of the metal and decreasing bulk of the anion but is independent from cisoid or transoid arrangement of the anions. From the homologous series of complexes presented three structure determining factors can be deduced:  (i) dicationic size; (ii) bent X−M−X (M = Sr, Ba) arrangement; (iii) increasing π interaction with increasing mass of the alkaline earth metal cation

Syntheses and Structures of Main Group Metal Complexes of the S(N<i>^t</i>Bu)₃^2- Dianion, an Inorganic Y-Conjugated Tripod

The metal metathesis reactions of [Li4{(NtBu)3S}2], 1, with various main group metal compounds are investigated. The reactions of 1 with group 14 metal(II) halides result in decomposition of the S(NtBu)32- dianion and subsequent formation of cubane-type structures of the metal tert-butylamides. In the reaction of GeCl2 with 1 a GeS double bond is formed. While the use of 1·thf initiates a complex redox reaction affording the mixed-valence Ge(II)/Ge(IV) complex [Ge4(S)(NtBu)4], 2, partial metal metathesis is achieved by employing metal(II) bis[bis(trimethylsilyl)amides] in reactions with 1. The mixed-metal complexes [(thf)2CaLi2{(NtBu)3S}2], 3, [(thf)2Ba2Li{N(SiMe3)2}{(NtBu)3S}2], 4, and [(thf)LiSn{N(SiMe3)2}{(NtBu)3S}], 5, were synthesized and structurally investigated. A closer inspection of the structural parameters of the complexes 3−5 reveals some of the intriguing ligand properties of the S(NtBu)32- dianion like the flexible electronic structure, the favorable cap-shaped geometry, and the Lewis base character of the central sulfur atom

Structural and Variable-Temperature NMR Studies of 9-Diisopropylphosphanylanthracenes and 9,10-Bis(diisopropylphosphanyl)anthracenes and Their Oxidation Products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature 1H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature 1H NMR spectra to be 56 kJ mol−1 (ΔG298K). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature

Structural and Variable-Temperature NMR Studies of 9-Diisopropylphosphanylanthracenes and 9,10-Bis(diisopropylphosphanyl)anthracenes and Their Oxidation Products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature 1H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature 1H NMR spectra to be 56 kJ mol−1 (ΔG298K). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature

Structural and Variable-Temperature NMR Studies of 9-Diisopropylphosphanylanthracenes and 9,10-Bis(diisopropylphosphanyl)anthracenes and Their Oxidation Products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature 1H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature 1H NMR spectra to be 56 kJ mol−1 (ΔG298K). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature

Structural and Variable-Temperature NMR Studies of 9-Diisopropylphosphanylanthracenes and 9,10-Bis(diisopropylphosphanyl)anthracenes and Their Oxidation Products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature 1H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature 1H NMR spectra to be 56 kJ mol−1 (ΔG298K). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature

Structural and Variable-Temperature NMR Studies of 9-Diisopropylphosphanylanthracenes and 9,10-Bis(diisopropylphosphanyl)anthracenes and Their Oxidation Products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature 1H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature 1H NMR spectra to be 56 kJ mol−1 (ΔG298K). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature

Structural and Variable-Temperature NMR Studies of 9-Diisopropylphosphanylanthracenes and 9,10-Bis(diisopropylphosphanyl)anthracenes and Their Oxidation Products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature 1H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature 1H NMR spectra to be 56 kJ mol−1 (ΔG298K). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature

Structural and Variable-Temperature NMR Studies of 9-Diisopropylphosphanylanthracenes and 9,10-Bis(diisopropylphosphanyl)anthracenes and Their Oxidation Products

The diisopropylphosphanyl-substituted anthracenes i-Pr2P(C14H9) (1a), i-Pr2P(C14H8)Br (2a), and (i-Pr2P)2(C14H8) (3a) and some of their oxidation products were prepared from 9-bromoanthracene and 9,10-dibromoanthracene, respectively. Low-temperature 1H NMR spectra of the 9-monophosphanyl-substituted anthracenes 1a and 2a are in accordance with a staggered conformer, while above room temperature dynamic processes occur. The low-temperature NMR spectrum of the 9,10-diphosphanylanthracene 3a indicates the presence of two different rotational isomers. The rotational barrier for 1a was determined from variable-temperature 1H NMR spectra to be 56 kJ mol−1 (ΔG298K). The crystal structure determinations show the solid-state conformers to be consistent with the prevailing conformer at low temperature