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The dialkyl malonate derived 1,3‐diphosphines R₂C(CH₂PPh₂)₂(R=a, Me;b, Et;c,n‐Bu;d,n‐Dec;e, Bn;f,p‐tolCH₂) are combined with (p‐tol₃P)₂PtCl₂ortrans‐(p‐tol₃P)₂Pt((C≡C)₂H)₂to give the chelatescis‐(R₂C(CH₂PPh₂)₂)PtCl₂(2 a–f, 94–69 %) orcis‐(R₂C(CH₂PPh₂)₂)Pt((C≡C)₂H)₂(3 a–f, 97–54 %). Complexes3 a–dare also available from2 a–dand excess 1,3‐butadiyne in the presence of CuI (cat.) and excess HNEt₂(87–65 %). Under similar conditions,2and3react to give the title compounds [(R₂C(CH₂PPh₂)₂)[Pt(C≡C)₂]₄(4 a–f; 89–14 % (64 % avg)), from which ammonium salts such as the co‐product [H₂NEt₂]⁺Cl⁻are challenging to remove. Crystal structures of4 a,bshow skew rhombus as opposed to square Pt₄geometries. The NMR and IR properties of4 a–fare similar to those of mono‐ or diplatinum model compounds. However, cyclic voltammetry gives only irreversible oxidations. As compared to mono‐platinum or Pt(C≡C)₂Pt species, the UV‐visible spectra show much more intense and red‐shifted bands. Time dependent DFT calculations define the transitions and principal orbitals involved. Electrostatic potential surface maps reveal strongly negative Pt₄C₁₆cores that likely facilitate ammonium cation binding. Analogous electronic properties of Pt₃C₁₂and Pt₅C₂₀homologs and selected equilibria are explored computationally.

 

Reactions of (O=)PH(OCH₂CH₃)₂and BrMg(CH₂)_mCH=CH₂(4.9–3.2 equiv;m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH₂)_mCH=CH₂]₂(2 a–c; 77–81 % after workup), which are treated with NaH and then α,ω‐dibromides Br(CH₂)_nBr (0.49–0.32 equiv;n=8 (a′), 10 (b′), 12 (c′), 14 (d′)) to yield the bis(trialkylphosphine oxides) [H₂C=CH(CH₂)_m]₂P(=O)(CH₂)_n(O=)P[(CH₂)_mCH=CH₂]₂(3 ab′,3 bc′,3 cd′,3 ca′; 79–84 %). Reactions of3 bc′and3 ca′with Grubbs’ first‐generation catalyst and then H₂/PtO₂afford the dibridgehead diphosphine dioxides(4 bc′,4 ca′; 14–19 %,n′=2m+2);³¹P NMR spectra show two stereoisomeric species (ca. 70:30). Crystal structures of two isomers of the latter are obtained,out,out‐4 ca′and a conformer ofin,out‐4 ca′that features crossed chains, such that the (O=)P vectors appearout,out. Whereas4 bc′resists crystallization, a byproduct derived from an alternative metathesis mode, (CH₂)₁₂P(=O)(CH₂)₁₂(O=)P(CH₂)₁₂, as well as3 ab′and3 bc′, are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.

 

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 2 ) 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. 

Three routes are explored to the title halide/cyanide complexes trans -Fe(CO)(NO)(X)(P((CH 2 ) 14 ) 3 P) ( 9c-X ; X = Cl/Br/I/CN), the Fe(CO)(NO)(X) moieties of which can rotate within the diphosphine cages (Δ H ‡ /Δ S ‡ (kcal mol −1 /eu −1 ) 5.9/−20.4 and 7.4/−23.9 for 9c-Cl and 9c-I from variable temperature 13 C NMR spectra). First, reactions of the known cationic complex trans -[Fe(CO) 2 (NO)(P((CH 2 ) 14 ) 3 P)] + BF 4 − and Bu 4 N + X − give 9c-Cl /- Br /- I /- CN (75–83%). Second, reactions of the acyclic complexes trans -Fe(CO)(NO)(X)(P((CH 2 ) m CHCH 2 ) 3 ) 2 and Grubbs’ catalyst afford the tris(cycloalkenes) trans -Fe(CO)(NO)(X)(P((CH 2 ) m CHCH(CH 2 ) m ) 3 P) ( m /X = 6/Cl,Br,I,CN, 7/Cl,Br, 8/Cl,Br) as mixtures of Z / E isomers (24–41%). Third, similar reactions of trans -[Fe(CO) 2 (NO)(P((CH 2 ) m CHCH 2 ) 3 ) 2 ] + BF 4 − and Grubbs’ catalyst afford crude trans -[Fe(CO) 2 (NO)P((CH 2 ) m CHCH(CH 2 ) m ) 3 P)] + BF 4 − ( m = 6, 8). However, the CC hydrogenations required to consummate routes 2 and 3 are problematic. Crystal structures of 9c-Cl /- Br /- CN are determined. Although the CO/NO/X ligands are disordered, the void space within the diphosphine cages is analyzed in terms of horizontal and vertical constraints upon Fe(CO)(NO)(X) rotation and the NMR data. The molecules pack in identical motifs with parallel P–Fe–P axes, and without intermolecular impediments to rotation in the solid state.