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 NHCMe (NHC=N-heterocyclic carbene) (4 a), H2 PBH2 NHCdipp (5 a) and tBuHPBH2 NHCMe (4 c) were determined. DFT calculations support the experimentally observed reaction behavior.

CpPEt2 As4 -An Organic-Substituted As4 Butterfly Compound.

CpPEt2 As4 (CpPEt =C5 (4-EtC6 H4 )5 ) (1) is synthesized by the reaction of CpPEt. radicals with yellow arsenic (As4 ). In solution an equilibrium of the starting materials and the product is found. However, 1 can be isolated and stored in the solid state without decomposition. As4 can be easily released from 1 under thermal or photochemical conditions. From powder samples of CpPEt2 As4 , yellow arsenic can be sublimed under rather mild conditions (T=125 °C). A similar behavior for the P4 -releasing agent was determined for the related phosphorus compound CpBIG2 P4 (2; CpBIG =C5 (4-nBuC6 H4 )5 ). DFT calculations show the importance of dispersion forces for the stability of the products.

Anionic Chains of Parent Pnictogenylboranes.

We report on the synthesis and structural characterization of unprecedented anionic parent compounds of mixed Group 13/15 elements. The reactions of the pnictogenylboranes H2 E-BH2 ⋅NMe3 (1 a=P, 1 b=As) with phosphorus and arsenic centered nucleophiles of the type [EH2 ]- (E=P, As) lead to the formation of compounds of the type [H2 E-BH2 -E'H2 ]- (2: E=E'=P; 3: E=E'=As; 4: E=P, E'=As) containing anionic pnictogen-boron chain-like units. Furthermore, a longer 5-membered chain species [H2 As-BH2 -PH2 -BH2 -AsH2 ]- (5) and a cyclic compound [NHCdipp -H2 B-PH2 -BH2 -NHCdipp ]+ [P5 B5 H19 ]- (6) containing a n-butylcyclohexane-like anion were obtained. All the compounds have been characterized by X-ray structure analysis, multinuclear NMR spectroscopy, IR spectroscopy, and mass spectrometry. DFT calculations elucidate their high thermodynamic stability, the charge distribution, and give insight into the reaction pathway.

Metal-Free Addition/Head-to-Tail Polymerization of Transient Phosphinoboranes, RPH-BH2: A Route to Poly(alkylphosphinoboranes).

Mild thermolysis of Lewis base stabilized phosphinoborane monomers R(1)R(2)P-BH2⋅NMe3 (R(1),R(2)=H, Ph, or tBu/H) at room temperature to 100 °C provides a convenient new route to oligo- and polyphosphinoboranes [R(1)R(2)P-BH2]n. The polymerization appears to proceed via the addition/head-to-tail polymerization of short-lived free phosphinoborane monomers, R(1)R(2)P-BH2. This method offers access to high molar mass materials, as exemplified by poly(tert-butylphosphinoborane), that are currently inaccessible using other routes (e.g. catalytic dehydrocoupling).

Cationic chains of phosphanyl- and arsanylboranes.

Whilst catena-phosphorus cations have been intensively studied in the last years, mixed Group 13/15 element cationic chains have not yet been reported. Reaction of the pnictogenboranes H2EBH2⋅NMe3 (E=P, As) with monohalideboranes lead to the cationic chain compounds [Me3N⋅BH2EH2BH2⋅NMe3][X] (E=P, As; X=AlCl4 , I) and [Me3N⋅BH2PH2BH2PH2BH2⋅NMe3][X] (X=I, VCl4(thf)2), respectively. All of the compounds have been characterized by X-ray structure analysis, NMR spectroscopy, IR spectroscopy, and mass spectrometry. DFT calculations elucidate the reaction pathway, the high thermodynamic stability, the charge distribution within the chain and confirm the observed solid-state structures.

The Lewis Base Stabilized Parent Arsanylborane H2AsBH2⋠NMe3.

Exclusively hydrogen-substituted arsanylboranes: The synthesis of the unprecedented Lewis base stabilized monomeric parent compound of the arsanylborane H2AsBH2⋅NMe3 was achieved in a one-pot reaction in high yield and purity. The analogous phosphanylborane was synthesized in a similar manner. A series of different reactions was performed on H2AsBH2⋅NMe3 to show its broad reactivity pattern.