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

Tuning Decomposition Temperature: A Structural Study of Ligand Directed Bonding and Fluxionality

In the first study of its kind towards the design and synthesis of easy-to-handle aluminium precursors that decompose at temperatures <200 °C: informed ligand choice and structural design of the compounds has caused inbuilt fluxionality leading to a markable decrease in the onset of decomposition temperatures. Eight thiourea ligands [L1H-L8H] were chosen with the steric bulk on the N atoms of these ligands varied systematically [L1-4H: RN(H)CS(NMe2) and L5-8H: RN(H)CS(NEt2); R=Me (L1H and L5H), Et (L2H and L6H), iPr (L3H and L7H) and Ph (L4H and L8H). Three families of aluminium compounds were synthesised by the reaction of these thiourea ligands with trimethylamine alane [Al(Lx)3 (1-7), trimethylaluminium [MeAl(Lx)2] (8-11) and triethylaluminium [EtAl(Lx)2] (12-14) respectively. The three most spatially encumbered compounds (Al(L3)3 (2), Al(L6)3 (5) and Al(L7)3 (6) are highly fluxional in solution and displayed lengthening of the Al-N bond as compared to the other compounds. Both factors directly affect the activation temperature of these compounds. The remaining compounds were not shown to display any of these behaviours and consequently have higher thermal decomposition temperatures. SCXRD, 1H and 13C{1H} NMR, variable temperature 1H NMR, MS and EA have been used to study the structure and solution dynamics of 1-14. This has directly been linked to the decomposition profiles of the compounds to assess their viability as precursors, evidencing that what we see in the solution state is present in the solid state too. Density functional theory calculations have been carried out to elucidate the various bonding modes observed for compounds 1-7. Tandem MS has been employed to better understand the breakdown of the molecules.

Synthesis and Reactivity of Germyl-Substituted Gallapnictenes

Decarbonylation of the phospha- and arsaketenyl germylenes (L)GeECO (E = P, As; L = CH[C(Me)NAr]2, Ar = 2,6-iPr2C6H3) in the presence of the Ga(I) precursor (L)Ga afforded the corresponding germyl-substituted gallaphosphene 1 and gallaarsene 3, respectively. Both 1 and 3 are examples of unsaturated chains with heavier group 13/15/14 elements. The germylene center and the polarized Pn = Ga (Pn = P or As) double bond provide multiple sites for small-molecule activation. For example, gallaarsene 3 reacted with adamantyl azide in a formal [3 + 2]-cyclization to give 4 containing a GaAsN3 heterocycle, clearly underlining the analogy between the As = Ga and C-C multiple bonds. By contrast, the reaction of 3 with Me-I afforded the 1,3-addition product 5, which indicates frustrated Lewis pair character in 3. DFT calculations indicate that the Ga-P/As bonds are highly polarized toward the pnictogen center. EDA-NOCV calculations further support this description and additionally shed light on ambiguous bonding scenarios in 4 and 5. These calculations prove that orbital interactions are outweighed by electrostatic interactions, resulting in polar bonds with significant ionic character.

Synthesis of bismuthanyl-substituted monomeric triel hydrides

The syntheses and characterizations of the first bismuthanylborane monomers stabilized only by a donor in D·BH2Bi(SiMe3)2 (D = DMAP 1a, IDipp 1b, IMe41c; DMAP = 4-dimethylaminopyridine, IDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene, IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) are presented. All compounds were synthesized by salt metathesis reactions between D·BH2I and KBi(SiMe3)2(THF)0.3 and represent some of the extremely rare compounds featuring a 2c-2e B-Bi bond in a molecular compound. The products display high sensitivity towards air and light and slowly decompose in solution even at -80 °C. By the reaction of IDipp·GaH2(SO3CF3) with KBi(SiMe3)2(THF)0.3, the synthesis of the first bismuthanylgallane IDipp·GaH2Bi(SiMe3)2 (2) stabilized only by a 2-electron donor was possible, as evident from single crystal X-ray structure determination, NMR spectroscopy and mass spectrometry. Computational studies shed light on the stability of the products and the electronic nature of the compounds.

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.

Unraveling the Steric Link to Copper Precursor Decomposition: A Multi-Faceted Study for the Printing of Flexible Electronics

The field of printed electronics strives for lower processing temperatures to move toward flexible substrates that have vast potential: from wearable medical devices to animal tagging. Typically, ink formulations are optimized using mass screening and elimination of failures; as such, there are no comprehensive studies on the fundamental chemistry at play. Herein, findings which describe the steric link to decomposition profile: combining density functional theory, crystallography, thermal decomposition, mass spectrometry, and inkjet printing, are reported. Through the reaction of copper(II) formate with excess alkanolamines of varying steric bulk, tris-co-ordinated copper precursor ions: "[CuL₃ ]," each with a formate counter-ion (1-3) are isolated and their thermal decomposition mass spectrometry profiles are collected to assess their suitability for use in inks (I^1-3 ). Spin coating and inkjet printing of I^1,2 provides an easily up-scalable method toward the deposition of highly conductive copper device interconnects (ρ = 4.7-5.3 × 10^-7 Ω m; ≈30% bulk) onto paper and polyimide substrates and forms functioning circuits that can power light-emitting diodes. The connection among ligand bulk, coordination number, and improved decomposition profile supports fundamental understanding which will direct future design.

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.