Assembly of a Triple-Cage Species Containing B, P, and Si Atoms

Abstract

Interest in inorganic ring and cage compounds containing boron and phosphorus atoms continues to expand and diversify. [1][2][3] In particular, our group has been interested in developing general assembly approaches for B x P y E z cage compounds that would permit a wide latitude in the selection of element stoichiometries and resultant cage sizes and structures. At this point, syntheses have been developed for bicyclic cages of the type P 2 (R 2 NB) 3 , 4 P 2 (R 2 NB) 2 SiR 2 , 5 P 2 (R 2 NB) 2 GeR 2 , 6 P 2 (R 2 NB) 2 SnR 2 , 7 and P 2 (R 2 -NB) 2 (SiR 2 ) 2 . 5 We report here an extension of this chemistry that leads to isolation of an unprecedented triple-cage molecule, P 6 ( i Pr 2 NB) 6 Si 2 (1), containing 14 atoms in the cage core.Compound 1 is obtained as pale yellow crystals from the 4:1 combination of i Pr 2 NBP(H)( i Pr 2 NB)PLi‚DME with Si 2 Cl 6 in hexane. 8 The compound is stable in dry air but slowly hydrolyzes in water or wet solvents. The composition of the molecule is confirmed by CHN analysis and high-resolution FAB-MS, which shows an intense envelope of ions in the region m/e 904-912 corresponding to the parent species. The molecular structure of 1 was deduced from single-crystal X-ray diffraction analysis, 9 and a view of the molecule is shown in Figure 1. The structure consists of a bicyclic P 2 B 2 Si 2 cage and two P 2 B 2 Si bicyclic cages, which share the two silicon atoms and are joined through a Si-Si bond. The P(1)B(1)P(2)B(2) four-membered ring in the P 2 B 2 Si 2 fragment is slightly folded (fold angle 17.0°) away from the Si-Si vector, and the two P 2 B 2 Si fragments are nearly eclipsed: the angle between the P(1)Si(1)Si(2) and P(2)Si(1)Si(2) planes is 10.9°. The metrical parameters for the bicyclic units are similar to those previously reported for the five-atom cage P 2 ( i Pr 2 NB) 2 SiPh 2 (2) 5 and the six-atom cage P 2 ( i Pr 2 NB) 2 Si 2 Me 4 (3). 5 The Si(1)-Si(2) bond length, 2.273(2) Å, is in the single-bond range but is considerably shorter than the value in 3, 2.352(2) Å. The average P-Si distances in the P 2 B 2 Si fragment, 2.262 Å, and in the P 2 B 2 Si 2 fragment, 2.267 Å, are identical to the average distance in 3 but slightly longer than that in 2, 2.244 Å. The average P-B bond lengths in the P 2 B 2 Si fragment and P 2 B 2 Si 2 fragment are identical, 1.964 Å (range 1.947(6)-1.984(7) Å), and these compare with 1.973 Å in 2 and 1.978 Å in 3. There is likely a larger strain energy involved in the P 2 B 2 Si cage fragments than in the P 2 B 2 Si 2 fragment, as suggested by differences in internal angles (e.g., the average sum of angles about the P atoms in the P 2 B 2 Si fragments is 212.9°compared to the sum in P 2 B 2 -Si 2 , 254.8°). The NMR spectra for 1 are consistent with this structure. The 31 P{ 1 H} NMR spectrum shows two resonances at δ 9 and -59 in a 2:1 area ratio that are assigned to the P atoms in the P 2 B 2 Si and P 2 B 2 Si 2 fragments, respectively. These shifts may be compared with values for the five-atom cage 2, 5 δ -18.4, and the six-atom ...

Ba3Zr2S7, the Low-Temperature Polymorph

“…The Zr--S distances range from 2.4972 (3) to 2.5557 (7) ,~,, where the long Zr--S2 contact of 2.5557 (7),~ is distal to the BaS layer. This behavior is the same as all of the other Ban+lZrnS3n+l compounds that have been characterized by single crystal X-ray diffraction (Chen& Eichhorn, 1991;Chen, Eichhorn & Fanwick, 1992;Chen, Wong-Ng & Eichhom, 1993;Chen, Eichhorn & Wong-Ng, 1994) but contrasts with the Ba3ZraS7 structure reported by Saeki et al (1991). The Ba--S contacts are in the range 3.1857 (13)-3.697 (2)~, with a short contact of 3.0833 (15) ,~, between Bal and $3.…”

Syntheses and Structures of Bis(azido)- and Bis(tert-butoxy)cyclodistibazanes

“…cyclobutane) but are also often formed in preference to their acyclic counterparts. This is especially true for heterocycles of the types (E−N) 2 , or (E−E‘) 2 , where E and E‘ are main-group elements. Interest in these ring systems has increased in the recent past, mainly because such species are good starting materials for polycyclic inorganic and organometallic compounds. , Like their carbon analogues, however, these inorganic rings do exhibit cis−trans isomerism, which may impact their applications.…”

Formation of Cage Compounds Containing Boron, Phosphorus, and Transition Metal Atoms

“…Molecules 2 and 4 possess a 2-fold rotation axis that passes through the Pd/Pt atom and the centroid of the folded B 2 P 2 ring. The general structural features of the compounds, (R 3 P) 2 M(PBNR 2 ) 2 , are similar to the platino compound 6 2 and the main group analogs, R 2 E(PBNR 2 ) 2 , − R 2 E = R 2 Si, R 2 Ge, and R 2 Sn, except that the M atoms are in square planar environments rather than tetrahedral.

2 Molecular structure and atom-labeling scheme for P 2 (tmpB) 2 Pd(PEt 3 ) 2 ( 3 ).

3 Molecular structure and atom-labeling scheme for P 2 ( i Pr 2 NB) 2 Pt(PEt 3 ) 2 ( 4 ).

…”

“…Recently, two approaches have been established for assembly of cage compounds containing boron and phosphorus atoms. − One method involves addition of unsaturated carbenoid fragments ER n , e.g., SnR 2 , to the bicyclic compound [(tmp)BP] 2 , as illustrated in eq 1. In a similar fashion, zerovalent (Ph 3 P) 2 Pt(C 2 H 4 ) undergoes oxidative addition to the P−P bond in the [(tmp)BP] 2 bicycle producing the cage species [(tmp)BP] 2 Pt(PPh 3 ) 2 . The use of (Ph 3 P) 4 Pd, however, produces other classes of metalated borylphosphanes .…”

“…This chemistry is shown in general in Scheme . Several families of cage compounds, (R 2 NBP) 2 ER n (ER n = BNR‘ 2 , SiR‘ 2 , GeR‘ 2 , SnR‘ 2 , and (SiMe 2 ) 2 ,), [(R 2 NBP) 2 ] 2 Si, and [(R 2 NBP) 2 ] 3 Si 2 , have now been synthesized in this manner, each in high yield. In this report, further extensions of this chemistry are described which result in the isolation of cage compounds containing boron, phosphorus, and transition metal (Ni, Pd, or Pt) atoms.…”