Characterization of the Ligand Properties of Donor-stabilized Pnictogenyltrielanes

A general synthesis and the characterization of novel alkyl-substituted NHC-stabilized pnictogenylboranes NHC ⋅ BH2 ER2 (NHC=N-heterocyclic carbene, E=P, As; R2 =Me2 , Ph2 , t BuH, Cy2 , (SiMe3 )2 ) are reported. These compounds were reacted with Ni(CO)4 to the corresponding complexes of the type [(NHC ⋅ BH2 ER2 )Ni(CO)3 ] to determine their donor strength by Tolman Electronic Parameters (TEPs) and their steric demand as ligands compared to classical phosphines, superbasic phosphines and other commonly applied donor systems. The results show that the NHC-stabilized pnictogenyltrielanes can be considered as being highly basic, while their steric influence depends strongly on the organic residues as well as the donor attached to the {BH2 } moiety. Although weaker than commonly used superbasic phosphines, the donor strength of pnictogenyltrielanes in general can be classified as of similar strength as NHCs. The steric and electronic properties can easily be modified by alkyl substitution as evident from the TEP trends.

NHC-Stabilized Mixed Group 13/14/15 Element Hydrides

The syntheses of novel N-heterocyclic carbene (NHC) adducts of group 13, 14 and 15 element hydrides are reported. Salt metathesis reactions between NaPH2 and IDipp ⋅ GeH2 BH2 OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) led to mixtures of the two isomers IDipp ⋅ GeH2 BH2 PH2 (2 a) and IDipp ⋅ BH2 GeH2 PH2 (2 b); by altering the reaction conditions an almost exclusive formation of 2 b was achieved. Attempts to purify mixtures of 2 a and 2 b by re-crystallization from THF afforded a salt [IDipp ⋅ GeH2 BH2  ⋅ IDipp][PHGeH2 BH2 PH2 BH2 GeH2 ] (4) that contains the novel anionic cyclohexyl-like inorganic heterocycle [PHGeH2 BH2 PH2 BH2 GeH2 ]- . In addition, the borane adducts IDipp ⋅ GeH2 BH2 PH2 BH3 (3 a) and IDipp ⋅ BH2 GeH2 PH2 BH3 (3 b) as even longer chain compounds were obtained from reactions of 2 a/2 b with H3 B ⋅ SMe2 and were studied by NMR spectroscopy. Accompanying DFT computations give insight into the mechanism and energetics associated with 2 a/2 b isomerization as well as their decomposition pathways.

A General Pathway towards NHC ⋅ GaH2 (OTf) Adducts - The Key for the Synthesis of NHC-Stabilized Cationic 13/15 Chain Compounds of Gallium

A general pathway towards NHC (NHC=N-heterocyclic carbene)-stabilized galliummonotriflates NHC ⋅ GaH2 (OTf) (NHC=IDipp, 1 a; IPr2 Me2 , 1 b; IMes, 1 c; IDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene, IPr2 Me2 =1,3-bis-(diisopropyl)-4,5-dimethyl-imidazolin-2-ylidene, IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) is reported. Quantum chemical calculations give detailed insight into the underlying reaction pathway. The obtained NHC ⋅ GaH2 (OTf) compounds were employed in reactions with donor-stabilized pnictogenylboranes to synthesize the elusive cationic parent 13/15/13 chain compounds [IDipp ⋅ GaH2 ER2 E'H2  ⋅ D][OTf] (3 a: D=IDipp, E=P, E'=B, R=H; 3 b: D=NMe3 , E=P, E'=B, R=H, 3 c: D=NMe3 , E=P, E'=B, R=Ph, 3 d: D=IDipp, E=P, E'=Ga, R=H). Supporting computational studies highlight the electronic features of the products.

Three- and Five-Membered Anionic Chains of Pnictogenylboranes

An unprecedented family of three- and five-membered substituted anionic derivatives of parent pnictogenylboranes is herein reported. Reacting various combinations of the pnictogenylboranes H₂ E'-BH₂ -NMe₃ (E'=P, As) with pnictogen-based nucleophiles MER1R2 (E=P, As; R1=H, R2=^t Bu; R1=R2=Ph; M=Na, K) allows for the isolation of the unsymmetrical products [Na(18-crown-6)][H₂ E'-BH₂ -EH^t Bu] (3: E=E'=P; 4: E=E'=As; 5: E=As, E'=P) and [M(C)][H₂ E'-BH₂ -EPh₂ ] (7: E=E'=P, M=Na, C=18-crown-6; 8: E=E'=As; M=K, C=[2.2.2]cryptand; 9: E=P, E'=As, M=Na, C=[2.2.2]cryptand; 10: E=As, E'=P, M=K, C=[2.2.2]cryptand). [Na(18-crown-6)][H₂ As-BH₂ -^t BuPH-BH₃ ] (6) is only accessible by a different pathway, using ^t BuPH₂ , BH₃  ⋅ SMe₂ and NaNH₂ as starting materials. Additionally, the synthesis of symmetrical diphenyl-substituted compounds [M(18-crown-6)][Ph₂ E-BH₂ -EPh₂ ] (11: E=P, M=Na; 12: E=As, M=K) is reported which can be regarded as isostructural inorganic, negatively charged analogs of dppm (1,1-bis(diphenylphosphino)methane) and dpam (1,1-bis(diphenylarsino)methane). Furthermore, an elongation of the pnictogen boron backbone in compounds 3, 7 and 9' (similar compound to 9, stabilized however by 18-crown-6), is attainable by reacting them with the pnictogenylboranes H₂ E'-BH₂ -NMe₃ leading to corresponding five-membered chain-like compounds [Na(18-crown-6)][H₂ E-BH₂ -R1R2P-BH₂ -E'H₂ ] (E=E'=P, R1=H, R2=^t Bu (13); E=E'=P, R1=R2=Ph (14); E=E'=As, R1=R2=Ph (15); E=P, E'=As, R1=R2=Ph (16)). Finally, the thermodynamics of the reaction pathways were evaluated by quantum chemical computations.

A convenient route to mixed cationic group 13/14/15 compounds

The formation of novel cationic mixed main group compounds is reported revealing a chain composed of different elements of group 13, 14, and 15. Reactions of different pnictogenylboranes R₂EBH₂·NMe₃ (E = P, R = Ph, H; E = As, R = Ph, H) with the NHC-stabilized compound IDipp·GeH₂BH₂OTf (1) (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene) were carried out, yielding the novel cationic, mixed group 13/14/15 compounds [IDipp·GeH₂BH₂ER₂BH₂·NMe₃]⁺ (2a E = P; R = Ph; 2b E = As; R = Ph; 3a E = P; R = H; 3b E = As; R = H) by the nucleophilic substitution of the triflate (OTf) group. The products were analysed by NMR spectroscopy and mass spectrometry and for 2a and 2b also by X-ray structure analysis. Further reactions of 1 with H₂EBH₂·IDipp (E = P, As) resulted in the unprecedented parent complexes [IDipp·GeH₂BH₂EH₂BH₂·IDipp][OTf] (5a E = P; 5b E = As), which were studied by X-ray structure analysis, NMR spectroscopy and mass spectrometry. Accompanying DFT computations give insight into the stability of the formed products with respect to their decomposition.

The benefits of Cu Kβ radiation for the single-crystal X-ray structure determination of crystalline sponges

The crystalline sponge method facilitates the X-ray structure determination of samples that do not crystallize or are too sparsely available to afford viable crystallization. By including these materials in a metal-organic framework, the structure of the guest molecules can be determined. Some of the inherent difficulties of this method are discussed and the use of Cu Kβ radiation is presented as a simple and effective means to improve the quality of the diffraction data that can be obtained from a sponge crystal.

An NHC-Stabilized H2 GeBH2 Precursor for the Preparation of Cationic Group 13/14/15 Hydride Chains

The synthesis, characterization and reactivity studies of the NHC‐stabilized complex IDipp ⋅ GeH₂BH₂OTf (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) are reported. Nucleophilic substitution of the triflate (OTf) group in 1 by phosphine or arsine donors provides access to the cationic group 13/14/15 chains [IDipp ⋅ GeH₂BH₂ERR¹R²]⁺ (2 E=P; R, R¹=H; R²=^tBu; 3 E=P; R=H; R¹, R²=Ph; 4 a E=P; R, R¹, R²=Ph; 4 b E=As; R, R¹, R²=Ph). These novel cationic chains were characterized by X‐ray crystallography, NMR spectroscopy and mass spectrometry. Moreover, the formation of the parent complexes [IDipp ⋅ GeH₂BH₂PH₃][OTf] (5) and [IDipp ⋅ GeH₃][OTf] (6) were achieved by reaction of 1 with PH₃. Accompanying DFT computations give insight into the stability of the formed chains with respect to their decomposition.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

A new family of silver(i) complexes stabilised by the phosphanylborane (C6H5)2PBH2·N(CH3)3

By the reaction of the phosphanylborane Ph2PBH2·NMe3 with Ag[FAl{OC6F10(C6F5)}3] or Ag[BF4] first Ag(i) coordination compounds stabilized by phosphine-boranes were obtained.

Bidentate Phosphanyl- and Arsanylboranes

A new class of neutral bidentate ligands with pnictogenyl-functional sites has been obtained. The reaction of tmeda⋅(BH₂ I)₂ (1, tmeda=tetramethylethylendiamine) with different phosphanides yields the corresponding bidentate phosphanylboranes tmeda⋅(BH₂ PH₂ )₂ (2 a), tmeda⋅(BH₂ PPh₂ )₂ (2 b), and tmeda⋅(BH₂ tBuPH)₂ (2 c). This reaction strategy could be further extended to synthesize the first bidentate arsanylborane tmeda⋅(BH₂ AsPh₂ )₂ (3). Depending on the substituents on the phosphorus, these compounds form different Au^I complexes, to build either polymeric tmeda⋅(BH₂ PH₂ AuCl)₂ (4 a), or monomeric tmeda⋅(BH₂ PPh₂ AuCl)₂ (4 b) products. These compounds form also neutral oligomeric group 13/15 chain-like molecules by coordination to a boron moiety such as tmeda⋅(BH₂ PH₂ BH₃ )₂ (5 a) and tmeda⋅(BH₂ AsPh₂ BH₃ )₂ (5 b). DFT calculations provide insight into the differences between the syntheses of mono- and bidentate pnictogenylboranes.

Gold(I) Complexes Containing Phosphanyl- and Arsanylborane Ligands

The structural and photophysical properties of a series of new Au^I compounds have been studied. The reactions of AuCl(tht) with the phosphanyl- and arsanylboranes RR^' EBH₂ NMe₃ (E=P, As; R=H, Ph; R'=H, Ph, tBu) afford the complexes [AuCl(RR^' EBH₂ NMe₃ )]. In the solid state, [AuCl(H₂ PBH₂ NMe₃ )]₂ (2 a) is a dimer showing unsupported intermolecular aurophilic interactions with short Au⋅⋅⋅Au distances. In contrast, [AuCl(H₂ AsBH₂ NMe₃ )]_n (2 b) aggregates to form 1D chains. Organic substituents on the pnictogen atoms lead to discrete molecules in [AuCl(RR^' PBH₂ NMe₃ )] (2 c: R=H, R'=tBu; 2 d: R=R'=Ph). To increase the aurophilicity, the ionic homoleptic complexes [Au(RR^' EBH₂ NMe₃ )₂ ][AlCl₄ ] (3 a-d) have been synthesized, for which 3 a,b form chains in the solid state and exhibit luminescence. The emissions show a drastic redshift with temperature decrease, correlating with decreasing Au⋅⋅⋅Au distances. DFT calculations provide insight into the bonding situation of the products.

Depolymerization of Poly(phosphinoboranes): From Polymers to Lewis Base Stabilized Monomers

We report on depolymerization reactions of poly(phosphinoboranes). The cleavage of the polymers [H₂ PBH₂ ]_n (2 a), [tBuHPBH₂ ]_n (2 c), [PhHPBH₂ ]_n (2 e) and the oligomer [Ph₂ PBH₂ ]_n (2 b), with strong Lewis bases (LBs), in particular with NHCs, leads to the corresponding monomeric phosphanylboranes R¹ R² PBH₂ LB. It is observed that the depolymerization depends on the strength and stability of the LBs as well as on the substitution pattern of the poly(phosphinoboranes). The solid state structures of the monomeric phosphinoboranes H₂ PBH₂ NHC^Me (NHC=N-heterocyclic carbene) (4 a), H₂ PBH₂ NHC^dipp (5 a) and tBuHPBH₂ NHC^Me (4 c) were determined. DFT calculations support the experimentally observed reaction behavior.