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Xanthene-backbone FLPs featuring secondary borane functions -B(Ar X )H (where Ar X =C 6 F 5 (Ar F ) or C 6 Cl 5 (Ar Cl )) have been targeted through reactions of the dihydroboranes Me 2 S ⋅ BAr X H 2 with [4,5-xanth(PR 2 )Li] 2 (R=Ph, i Pr), and investigated in the synthesis of related cationic systems via hydride abstraction. The reactivity of these systems (both cationic and charge neutral) with ammonia have been probed, with a view to probing the potential for proton shuttling via N-H bond 'activation.' We find that in the case of four-coordinate boron systems (cationic or change neutral), the N-H linkage remains intact, supported by a NH⋅⋅⋅P hydrogen bond which is worth up to 17 kcal mol -1 thermodynamically, and enabled by planarization of the flexible xanthene scaffold. For cationic three coordinate systems, N-to-P proton transfer is viable, driven by the ability of the boron centre to stabilise the [NH 2 ] - conjugate base through N-to-B π bonding. This proton transfer can be shown to be reversible in the presence of excess ammonia, depending on the nature of the B-bound Ar X group. It is viable in the case of C 6 F 5 substituents, but is prevented by the more sterically encumbering and secondary donor-stabilising capabilities of the C 6 Cl 5 substituent., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

By exploiting the electronic capabilities of the N-heterocyclic boryloxy (NHBO) ligand, we have synthesized "naked" acyclic gallyl [Ga{OB(NDippCH) 2 } 2 ] - and indyl [In{OB(NDippCH) 2 } 2 ] - anions (as their [K(2.2.2-crypt)] + salts) through K + abstraction from [KGa{OB(NDippCH) 2 } 2 ] and [KIn{OB(NDippCH) 2 } 2 ] using 2.2.2-crypt. These systems represent the first O-ligated gallyl/indyl systems, are ultimately accessed from cyclopentadienyl Ga I /In I precursors by substitution chemistry, and display nucleophilic reactivity which is strongly influenced by the presence (or otherwise) of the K + counterion., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Bimetallic compounds containing direct metal-group 13 element bonds have been shown to display unprecedented patterns of cooperative reactivity towards small molecules, which can be influenced by the identity of the group 13 element. In this context, we present here a systematic appraisal of group 13 metallo-ligands of the type [(NON)E] - (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) for E=Al, Ga and In, through a comparison of structural and spectroscopic parameters associated with the trans L or X ligands in linear d 10 complexes of the types LM{E(NON)} and XM'{E(NON)}. These studies are facilitated by convenient syntheses (from the In(I) precursor, InCp) of the potassium indyl species [{K(NON)In}⋅KCp] n (1) and [(18-crown-6) 2 K 2 Cp] [(NON)In] (1'), and lead to the first structural characterisation of Ag-In and Hg-E (E=Al, In) covalent bonds. The resulting structural, spectroscopic and quantum chemical probes of Ag/Hg complexes are consistent with markedly stronger σ-donor capabilities of the aluminyl ligand, [(NON)Al] - , over its gallium and indium counterparts., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

While the nucleophilic addition of ammonia to ketones is an archetypal reaction in classical organic chemistry, the reactivity of heavier group 14 carbonyl analogues (R 2 E=O; E=Si, Ge, Sn, or Pb) with NH 3 remains sparsely investigated, primarily due to the synthetic difficulties in accessing heavier ketone congeners. Herein, we present a room-temperature stable boryl-substituted amidinato-silanone {(HCDippN) 2 B}{PhC(tBuN) 2 }Si=O (Dipp=2,6-iPr 2 C 6 H 3 ) (together with its germanone analogue), formed from the corresponding silylene under a N 2 O atmosphere. This system reacts cleanly with ammonia in 1,2-fashion to give an isolable sila-hemiaminal complex {(HCDippN) 2 B}{PhC(tBuN) 2 }Si(OH)(NH 2 ). Quantum chemical calculations reveal that the formation of this sila-hemiaminal is crucially dependent on the nature of the ancillary ligand scaffold. It is facilitated thermodynamically by the hemi-lability of the amidinate ligand (which allows for the formation of an energetically critical intramolecular N⋅⋅⋅HO hydrogen bond within the product) and is enabled mech-anistically by a process in which the silanone initially acts in umpolung fashion as a base (rather than an acid), due to the strongly electron-releasing and sterically bulky nature of the ancillary boryl ligand., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The reduction of the boryl-substituted Sn II bromide {(HCDippN) 2 B}Sn(IPrMe)Br with 1.5 equivalents of potassium graphite leads to the generation of the cyclic tetratin tetraboryl system K 2 [Sn 4 {B(NDippCH) 2 } 4 ], a homo-metallic heavier analogue of the cyclobutadiene dianion. This system is non-aromatic as determined by Nucleus Independent Chemical Shift Calculations (NICS(0)=-0.28, NICS(1)=-3.17), with the primary contributing resonance structures shown by Natural Resonance Theory (NRT) to involve a Sn=Sn double bond and 1,2-localized negative charges. Abstraction of the K + cations or oxidation leads to contraction or cleavage of the Sn 4 unit, respectively, while protonation generates the neutral dihydride 1,2-Sn 4 {B(NDippCH) 2 } 4 H 2 (a heavier homologue of cyclobutene) in a manner consistent with the predicted charge distribution in the [Sn 4 {B(NDippCH) 2 } 4 ] 2- dianion., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Boryltin compounds featuring the metal in the+1 or 0 oxidation states can be synthesized from the carbene-stabilized tin(II) bromide (boryl)Sn(NHC)Br (boryl={B(NDippCH) 2 }; NHC=C{(N i PrCMe) 2 }) by the use of strong reducing agents. The formation of the mono-carbene stabilized distannyne and donor-free distannide systems (boryl)SnSn(IPrMe)(boryl) (2) and K 2 [Sn 2 (boryl) 2 ] (3), using Mg(I) and K reducing agents mirrors related germanium chemistry. In contrast to their lighter congeners, however, systems of the type [Sn(boryl)] n are unstable with respect to disproportionation. Carbene abstraction from 2 using BPh 3 , and two-electron oxidation of 3 both result in the formation of a 2 : 1 mixture of the Sn(II) compound Sn(boryl) 2 , and the hexatin cluster, Sn 6 (boryl) 4 (4). A viable mechanism for this rearrangement is shown by quantum chemical studies to involve a vinylidene intermediate (analogous to the isolable germanium compound, (boryl) 2 Ge=Ge), which undergoes facile atom transfer to generate Sn(boryl) 2 and trinuclear [Sn 3 (boryl) 2 ]. The latter then dimerizes to give the observed hexametallic product 4, with independent studies showing that similar trigermanium species aggregate in analogous fashion., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

We report on the synthesis of a distannyne supported by a pincer ligand bearing pendant amine donors that is capable of reversibly activating E-H bonds at one or both of the tin centres through dissociation of the hemi-labile N-Sn donor/acceptor interactions. This chemistry can be exploited to sequentially (and reversibly) assemble mixed-valence chains of tin atoms of the type ArSn{Sn(Ar)H} n SnAr (n=1, 2). The experimentally observed (decreasing) propensity towards chain growth with increasing chain length can be rationalized both thermodynamically and kinetically by the electron- withdrawing properties of the -Sn(Ar)H- backbone units generated via oxidative addition., (© 2021 Wiley-VCH GmbH.)