Inorg. Chem. 1986, 25, 4382-4385
4382
Contribution from the Fakultat fur Chemie der Universitat Bielefeld, 4800 Bielefeld, Federal Republic of Germany, Fakultat fur Chemie der Universitat Bochum, 463 Bochum, Federal Republic of Germany, and Institut fur Organische Chemie der Universitat Essen, 4300 Essen, Federal Republic of Germany
Theoretical Studies on Inorganic Ring Systems. Tetraphosphabicyclobutane, Cyclotriphosphane, and White Phosphorus: Ring Strain and Hybridization Wolfgang W. Schoeller,*t Volker Staemmler,*t Paul Rademacher,! and Edgar Niecket R e c e i v e d March 26, 1986
The electronic nature of white phosphorus, cyclotriphosphane, and tetraphosphabicyclobutane is investigated by ab initio calculations at a double-l level and with inclusion of electron correlation. The photoelectron spectrum of the last compound is reported as well, the assignment of the bands being based on the results of the ab initio calculations. The analysis of localized orbitals reveals that in tetraphosphabicyclobutane the central bond has almost the same p character as the peripheral bonds. The bonding situation is similar to that in cyclotriphosphane but rather different from that in cyclopropane. In contrast to bicyclobutane, tetraphosphabicyclobutane and cyclotriphosphane are almost free of ring strain, as proven by corresponding isodesmic reactions.
Introduction
Table I. Energies of the Highest Molecular Orbitals of Parent 2 (R
Since Baeyer’ first studied deviations of carbon from tetrahedral valency, the electronic s t r u c t u r e of strained ring hydrocarbons h a s been t h e subject of increasing interest.2 Early attention focused on cyclopropane, as well documented in t h e classical contributions of Walsh,, Coulson and M ~ f f i t tand ,~ For~ter.A ~ later milestone in t h e understanding of the electronic n a t u r e of strained hydrocarbons is the detection of through-bond vs.
= H ) Obtained with the Various Basis Setsn
through-space interaction.6
i
basis I
basis I1
basis I11
0 1 2 3 4
5.61 (al) 6.24 (b,) 7.51 (az) 7.84 (b2) 7.93 (a,) 9.80 (b2) 12.50 (a,)
8.96 (al) 9.64 (b,) 10.90 (a2) 11.01 (b2) 11.51 (a,) 12.67 (bz) 15.31 (al)
8.91 (a,) 9.58 (b,) 10.83 (a2) 10.96 (b2) 11.46 (al) 12.61 (bz) 15.26 (al)
5
1
2
D
energy, eVb
HOMO
6
a Symmetry designations (in parentheses) are according to C I L . bNegative energies.
1 -
2 -
3 -
( I ) Basis I refers to a minimal GTO basis set for first- and second-row elements as developed by Pople et aLl1 (2) Basis I1 consists of Gaussian lobe functions.12 It is of double-{ quality, supplemented by polarization functions at phosphorus (DZ+P) and constructed from the following Huzinaga13 bases: C (7.3) in the contraction (4,3X1/2,l) N (8,4) in the contraction (5,3X1/3,1) P (l0,6,1) in the contraction (5,5X1/4,2XI/l); H (4) in the contraction (3,l)
6
= 0.5
-5
The chemistry of inorganic ring systems is very different from t h a t of carbon-hydrogen ring compounds. Their bonding properties are not well understood, although a large a m o u n t of experimental d a t a has been collected in recent reviews.’ I t is t h e purpose of this paper t o deal with the electronic structure of a number of phosphorus ring compounds.8 The following points will be discussed in detail: (a) interpretation of the photoelectron spectrum of 2 (R = N(SiMe,),) by means of ab initio calculations on 2 (R = H) and some of its derivatives (R = CH,, NH,); (b) Mulliken population analyses of 1-3 in terms of localized orbitals a n d a comparison with t h e strain-free compounds phosphine and diphosphine; (c) ring strain in 1-3 as obtained from studies of isodesmic reactions. T h e results obtained will be compared with the findings for analogous carbon-hydrogen systems, Le. cyclopropane (4) and bicyclobutane ( 5 ) . Theoretical Procedure Our analysis of the bonding in 1-3 is based on the results of ab initio S C F calculations. A few selected calculations were also performed with inclusion of electron correlation using the PNO-CI and CEPA s c h e m e ~ . ~ *The l ~ following basis sets were used for the ab initio calculations.
Universitat Bielefeld.
* Universitat Bochum. f
f’d
Universitat Essen.
0020-1669/86/1325-4382$01 S O / O
(1) Baeyer, A. Ber. Dtsch. Chem. Ges. 1885, 18, 2269.
(2) Greenberg, A.; Liebman, J. F. Strained Molecules: Academic: New York, 1978. Liebman, J. F.: Greenberg, A. Chem. Rev. 1976, 7 6 , 311. See also: Dill, J. D.; Greenberg, A.; Liebman, J. F. J . A m . Chem. SOC. 1979, 101, 6814. (3) Walsh, A. D. Trans. Farady S o t . 1946, 42, 56; 1947, 43, 60, 158; Discuss. Farady S o t . 1947, No. 2, 18. See also: Bent, H. A. Chem. Rea. 1961, 61, 275. Hoffmann, R. Tetrahedron Lett. 1970, 2907. Giinther, H. Tetrahedron Lett. 1970, 5173. (4) Coulson, C. A,; Moffitt, W. E. Philos. Mag. 1949, 40, 1. See also: Bernett, W. A. J. Chem. Educ. 1967, 44, 17. (5) Forster, Th. Z . Phys. Chem., Abt. B 1939, 43, 58. (6) Stohrer, W.-D.; Hoffmann, R. J . A m . Chem. SOC.1972, 94, 779. Klessinger, M. Elektronenstruktur organischer Molekule; Verlag Chemie: Weinheim, 1982. (7) (a) Baudler, M. Angew. Chem. 1982, 94, 520; Angew. Chem., Inr. E d . Engl. 1982,21,492. (b) Roesky, H. W. Adu. Inorg. Chem. Radiochem. 1979, 22, 239. (c) Keat, R. Top. Curr. Chem. 1982, 102, 89. (8) For previous contributionson the electronic properties of inorganic ring systems see: (a) Schoeller, W. W.; Dabisch, T. J . Chem. S o t . , Dalton Trans. 1983,241 1. (b) Schoeller, W. W.; Lerch, C. Inorg. Chem. 1983, 22. 2992. (9) Ahlrichs, R.; Lischka, H.; Staemmler, V.; Kutzelnigg, W. J. Chem. Phys. 1975, 62, 1225. (10) Meyer, W. Int. J. Quantum Chem. 1971,S5,341; J. Chem. Phys. 1973, 58. . 1017. .., .. (11) Hehre, W. J.; Stewart, R. F.; Pople, J . A. J . Cbem. Phys. 1969, 5 1 , 2657. Collins, J. B.; Schleyer, P. v. R.; Binkley, J . S.; Pople, J. A. J . Chem. Phys. 1976, 64, 5142. (1 2) The computer program used is described by: Ahlrichs, R. Tbeor. Chim. Acta 1974, 33, 157. See also ref 9. ( 1 3) Huzinaga, S. “Approximate Atomic Functions 11”; Technical Report; The University of Alberta, 1971.
0 1986 American Chemical Society
Theoretical Studies on Inorganic Ring Systems
Inorganic Chemistry, Vol. 25, No. 24, 1986 4383 Table 11. Energies of the Highest Molecular Orbitals of the Derivatives (R = NH2, C H J of 2, at the Basis I1 Level energy, eV"
HOMO
i
N H 2 (perpendicular) 8.58 (al) 8.78 (b2) 9.35 (bi) 10.40 (a2) 10.93 (al) 12.30 (al) 12.88 (b2)
0 1 2 3 4 5 6 a Negative
6
a
, 10
12
:i
16
la
I P lev1
Figure 1. The H e I photoelectron spectrum of 2 (R = N(SiMe,),
C as basis I1 N as basis I1 P (10,6,1) in the contraction (4,6X1/3,3Xl/l); = 0.65 H (4,l) in the contraction (3,1/1);
