(Phosphanyl)phosphaketenes as building blocks for novel phosphorus heterocycles

Although BH3 simply coordinates the endocyclic P of (phospholidino)phosphaketene 1Dipp , the bulkier B(C6F5)3 gives rise to a zwitterionic diphosphirenium, which is a novel type of 2π-electron aromatic system as shown by the calculated NICS values.


Synthesis and Characterization data Preparation of 4:
A mixture of 1 Dipp (30 mg, 0.064 mmol) and excess BH 3 -SMe 2 was dissolved in pentane (2 mL

S-16
Structure of 4 in the solid state. All hydrogen atoms, except for BH 3 , omitted for clarity

S-18
Structure of 5 in the solid state. All hydrogen atoms omitted for clarity

S-19
Xray Table 3 Crystal data and structure refinement for 6.

S-20
Structure of 6 in the solid state. All hydrogen atoms omitted for clarity.

S-21
Xray Structure could not be refined below 16%. Hence the corresponding data which only allowed us to confirm the formation of this species has not been submitted to the CCDC.

S-22
Structure of 7 in the solid state. All hydrogen atoms omitted for clarity

S-24
Structure of 8 in the solid state. All hydrogen atoms omitted for clarity.

S-26
Structure of 10 in the solid state. All hydrogen atoms omitted for clarity.

S-28
Structure of 10' in the solid state. All hydrogen atoms omitted for clarity.

Computational part
Calculations were carried out with the Gaussian 09 package 3 (version g09, rev.d01). Geometry optimizations were performed with the B3LYP 4 or M06-2X 5 functional. The def2-TZVP, 6-31G(d) 6 or cc-pVDZ basis sets were used for all the atoms. Frequency calculations at the same level of theory were performed to identify the number of imaginary frequencies ( Comment to Figure S1: Even though the activation barrier of Lewis-acid activation is fairly high (ΔG ‡ = 32.1 kcal/mol) it should be pointed out that the in reference (starting) molecule BF 3 is coordinated to the inner phosphorus of the [P]-PCO molecule. As this reaction also only proceeds when employing a bulky Lewis acidic borane such as B(C 6 F 5 ) 3 , in which this coordination is inhibited based on sterics, it seems reasonable to assume that the energies of transition state and product will significantly decrease.
S-31 Comment to Figure S2: The reaction pathway shows a low lying transition state (ΔG ‡ = 16.2 kcal/mol) for the attack of the endocyclic phosphorus onto the P-atom releasing CO in agreement with our recent proposed P-CO substitution approach. Even though the reaction is predicted to be slightly endergonic, the calculations do not take into account the sodium cation as well as any solvent effects. As the latter play a crucial role in solubilizing NaPCO and therefore increasing its reactivity, the relative stability of starting materials and products might strongly vary. However, the point of this calculation is to rationalize the observed reactivity and to give an energetically reasonable mechanism for the formation of the 4-membered "P -" insertion product.