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1. Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

   https://doi.org/10.3762/bjoc.14.211  

   Fiedler, Tobias ; Barbasiewicz, Michał ; Stollenz, Michael ; Gladysz, John A ( January 2018 , Beilstein Journal of Organic Chemistry)

   Two routes to the title compounds are evaluated. First, a ca. 0.01 M CH 2 Cl 2 solution of H 3 B·P((CH 2 ) 6 CH=CH 2 ) 3 ( 1 ·BH 3 ) is treated with 5 mol % of Grubbs' first generation catalyst (0 °C to reflux), followed by H 2 (5 bar) and Wilkinson's catalyst (55 °C). Column chromatography affords H 3 B·P( n- C 8 H 17 ) 3 (1%), H 3 B· P ((CH 2 ) 13 C H 2 )( n -C 8 H 17 ) (8%; see text for tie bars that indicate additional phosphorus–carbon linkages, which are coded in the abstract with italics), H 3 B· P ((CH 2 ) 13 C H 2 )((CH 2 ) 14 ) P ((CH 2 ) 13 C H 2 )·BH 3 ( 6 ·2BH 3 , 10%), in,out -H 3 B·P((CH 2 ) 14 ) 3 P·BH 3 ( in,out - 2 ·2BH 3 , 4%) and the stereoisomer ( in,in / out,out )- 2 ·2BH 3 (2%). Four of these structures are verified by independent syntheses. Second, 1,14-tetradecanedioic acid is converted (reduction, bromination, Arbuzov reaction, LiAlH 4 ) to H 2 P((CH 2more ») 14 )PH 2 ( 10 ; 76% overall yield). The reaction with H 3 B·SMe 2 gives 10 ·2BH 3 , which is treated with n -BuLi (4.4 equiv) and Br(CH 2 ) 6 CH=CH 2 (4.0 equiv) to afford the tetraalkenyl precursor (H 2 C=CH(CH 2 ) 6 ) 2 (H 3 B)P((CH 2 ) 14 )P(BH 3 )((CH 2 ) 6 CH=CH 2 ) 2 ( 11 ·2BH 3 ; 18%). Alternative approaches to 11 ·2BH 3 (e.g., via 11 ) were unsuccessful. An analogous metathesis/hydrogenation/chromatography sequence with 11 ·2BH 3 (0.0010 M in CH 2 Cl 2 ) gives 6 ·2BH 3 (5%), in,out - 2 ·2BH 3 (6%), and ( in,in / out,out )- 2 ·2BH 3 (7%). Despite the doubled yield of 2 ·2BH 3 , the longer synthesis of 11 ·2BH 3 vs 1 ·BH 3 renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses.« less
2. Bridging cyanides from cyanoiron metalloligands to redox-active dinitrosyl iron units

   https://doi.org/10.1039/C8DT01761A  

   Ghosh, Pokhraj ; Quiroz, Manuel ; Pulukkody, Randara ; Bhuvanesh, Nattamai ; Darensbourg, Marcetta Y. ( January 2018 , Dalton Transactions)

   Cyanide, as an ambidentate ligand, plays a pivotal role in providing a simple diatomic building-block motif for controlled metal aggregation (M–CN–M′). Specifically, the inherent hard–soft nature of the cyanide ligand, i.e. , hard-nitrogen and soft-carbon centers, is due to electronic handles for binding Lewis acids following the hard–soft acid–base principle. Studies by Holm and Karlin showed structural and electronic requirements for cyanide-bridged (por)Fe III –CN–Cu II/I (por = porphyrin) molecular assemblies as biomimetics for cyanide-inhibited terminal quinol oxidases and cytochrome-C oxidase. The dinitrosyliron unit (DNIU) that exists in two redox states, {Fe(NO) 2 } 9 and {Fe(NO) 2 } 10 , draws attention as an electronic analogy of Cu II and Cu I , d 9 and d 10 , respectively. In similar controlled aggregations, L-type [(η 5 -C 5 R 5 )Fe(dppe)(CN)] (dppe = diphenyl phosphinoethane; R = H and Me) have been used as N-donor, μ-cyanoiron metalloligands to stabilize the DNIU in two redox states. Two bimetallic [(η 5 -C 5 R 5 )(dppe)Fe II –CN–{Fe(NO) 2 } 9 (sIMes)][BF 4 ] complexes, Fe-1 (R = H) and Fe*-1 (R = CH 3 ), showed dissimilar Fe II CN–{Fe(NO) 2 } 9 angular bends due to the electronicmore »donor properties of the [(η 5 -C 5 R 5 )Fe(dppe)(CN)] μ-cyanoiron metalloligand. A trimetallic [(η 5 -C 5 Me 5 )(dppe)Fe II –CN] 2 –{Fe(NO) 2 } 10 complex, Fe*-2 , engaged two bridging μ-cyanoiron metalloligands to stabilize the {Fe(NO) 2 } 10 unit. The lability of the Fe II –CN–{Fe(NO) 2 } 9/10 bond was probed by suitable X-type (Na + SPh − ) and L-type (PMe 3 ) ligands. Treatment of Fe-1 and Fe*-1 with PMe 3 accounted for a reduction-induced substitution at the DNIU, releasing [(η 5 -C 5 R 5 )Fe(dppe)(CN)] and N-heterocyclic carbene, and generating (PMe 3 ) 2 Fe(NO) 2 as the reduced {Fe(NO) 2 } 10 product.« less
3. 14-Electron Rh and Ir silylphosphine complexes and their catalytic activity in alkene functionalization with hydrosilanes

   https://doi.org/10.1039/D1DT00677K  

   Abeynayake, Niroshani S. ; Zamora-Moreno, Julio ; Gorla, Saidulu ; Donnadieu, Bruno ; Muñoz-Hernández, Miguel A. ; Montiel-Palma, Virginia ( August 2021 , Dalton Transactions)

   Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh( iii ) devoid of agostic interactions. The complexes [X–Rh(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], where X = Cl (Rh-1), Br (Rh-2), I (Rh-3), OTf (Rh-4), Cl·GaCl 3 (Rh-5); derive from a bis(silyl)- o -tolylphosphine with isopropyl substituents on the Si atoms. All five complexes display a sawhorse geometry around Rh and exhibit similar spectroscopic and structural properties. The catalytic activity of these complexes and [Cl–Ir(κ 3 ( P,Si,Si )PhP( o -C 6 H 4 CH 2 Si i Pr 2 ) 2 ], Ir-1, in styrene and aliphatic alkene functionalizations with hydrosilanes is disclosed. We show that Rh-1 catalyzes effectively the dehydrogenative silylation of styrene with Et 3 SiH in toluene while it leads to hydrosilylation products in acetonitrile. Rh-1 is an excellent catalyst in the sequential isomerization/hydrosilylation of terminal and remote aliphatic alkenes with Et 3 SiH including hexene isomers, leading efficiently and selectively to the terminal anti-Markonikov hydrosilylation product in all cases. With aliphatic alkenes, no hydrogenation products are observed. Conversely, catalysis of the same hexene isomersmore »by Ir-1 renders allyl silanes, the tandem isomerization/dehydrogenative silylation products. A mechanistic proposal is made to explain the catalysis with these M( iii ) complexes.« less
4. Platinum( ii ) alkyl complexes of chelating dibridgehead diphosphines P((CH ₂ ) _n ) ₃ P ( n = 14, 18, 22); facile cis / trans isomerizations interconverting gyroscope and parachute like adducts

   https://doi.org/10.1039/D1DT02321G  

   Zhu, Yun ; Ehnbom, Andreas ; Fiedler, Tobias ; Shu, Yi ; Bhuvanesh, Nattamai ; Hall, Michael B. ; Gladysz, John A. ( September 2021 , Dalton Transactions)

   The gyroscope like dichloride complexes trans -Pt(Cl) 2 (P((CH 2 ) n ) 3 P) ( trans -2; n = c, 14; e, 18; g, 22) and MeLi (2 equiv.) react to yield the parachute like dimethyl complexes cis -Pt(Me) 2 (P((CH 2 ) n ) 3 P) ( cis -4c,e,g, 70–91%). HCl (1 equiv.) and cis -4c react to give cis -Pt(Cl)(Me)(P((CH 2 ) 14 ) 3 P) ( cis -5c, 83%), which upon stirring with silica gel or crystallization affords trans -5c (89%). Similar reactions of HCl and cis -4e,g give cis / trans -5e,g mixtures that upon stirring with silica gel yield trans -5e,g. A parallel sequence with trans -2c/EtLi gives cis -Pt(Et) 2 (P((CH 2 ) 14 ) 3 P) ( cis -6c, 85%) but subsequent reaction with HCl affords trans -Pt(Cl)(Et)(P((CH 2 ) 14 ) 3 P) ( trans -7c, 45%) directly. When previously reported cis -Pt(Ph) 2 (P((CH 2 ) 14 ) 3 P) is treated with HCl (1 equiv.), cis - and trans -Pt(Cl)(Ph)(P((CH 2 ) 14 ) 3 P) are isolated (44%, 29%), with the former converting to the latter at 100 °C. Reactions of trans -5c and LiBr or NaI affordmore »the halide complexes trans -Pt(X)(Me)(P((CH 2 ) 14 ) 3 P) ( trans -9c, 88%; trans -10c, 87%). Thermolyses and DFT calculations that include acyclic model compounds establish trans > cis stabilities for all except the dialkyl complexes, for which energies can be closely spaced. The σ donor strengths of the non-phosphine ligands are assigned key roles in the trends. The crystal structures of cis -4c, trans -5c, trans -7c, and trans -10c are determined and analyzed together with the computed structures.« less
5. Selective binding of anions by rigidified nanojars: sulfate vs. carbonate

   https://doi.org/10.1039/d1ob01318a  

   Al Isawi, Wisam A. ; Salome, Austin Z. ; Ahmed, Basil M. ; Zeller, Matthias ; Mezei, Gellert ( September 2021 , Organic & Biomolecular Chemistry)

   Selective binding and transport of highly hydrophilic anions is ubiquitous in nature, as anion binding proteins can differentiate between similar anions with over a million-fold efficiency. While comparable selectivity has occasionally been achieved for certain anions using small, artificial receptors, the selective binding of certain anions, such as sulfate in the presence of carbonate, remains a very challenging task. Nanojars of the formula [anion⊂{Cu(OH)(pz)} n ] 2− (pz = pyrazolate; n = 27–33) are totally selective for either CO 3 2− or SO 4 2− over anions such as NO 3 − , ClO 4 − , BF 4 − , Cl − , Br − and I − , but cannot differentiate between the two. We hypothesized that rigidification of the nanojar outer shell by tethering pairs of pyrazole moieties together will restrict the possible orientations of the OH hydrogen-bond donor groups in the anion-binding cavity of nanojars, similarly to anion-binding proteins, and will lead to selectivity. Indeed, by using either homoleptic or heteroleptic nanojars of the general formula [anion⊂Cu n (OH) n (L2–L6) y (pz) n −2 y ] 2− ( n = 26–31) based on a series of homologous ligands HpzCH 2 (CH 2 ) x CHmore »2 pzH ( x = 0–4; H 2 L2–H 2 L6), selectivity for carbonate (with L2 and with L4–L6/pz mixtures) or for sulfate (with L3) has been achieved. The synthesis of new ligands H 2 L3, H 2 L4 and H 2 L5, X-ray crystal structures of H 2 L4 and the tetrahydropyranyl-protected derivatives (THP) 2 L4 and (THP) 2 L5, synthesis and characterization by electrospray-ionization mass spectrometry (ESI-MS) of carbonate- and sulfate-nanojars derived from ligands H 2 L2–H 2 L6, as well as detailed selectivity studies for CO 3 2− vs. SO 4 2− using these novel nanojars are presented.« less