88 A Stable Monocyclic Triarylalkoxyhydridophosphorane A 10-P-5 Species with an A p i c a l P-H B o n d 1
MICHAEL R. ROSS and J. C. MARTIN Roger Adams Laboratory, University of Illinois, Urbana,IL61801
Spectroscopic data presented in an earlier report (1) were interpreted in terms of an apical P-H bond disposition and a t r i gonal bipyramidal (TBP) structure for a monocyclic triarylhydridophosphorane (1b). We have an X-ray crystallographic solution of the structure of apical hydridophosphorane 1a as well as the structure of its diaryldialkoxy spirobicyclic analogue, 2. Table I lists important bond lengths and angles for the two species, and, for comparison, the phosphatrane of Verkade (2), 3, and equatorial hydridophosphorane 9. Phosphorane 1a has a1JPHvalue (269 Hz in CDCl3) and an infrared P-H stretching frequency (2100 cm-1, CHCl3) that are sig nificantly smaller than the corresponding values for 2 (1JPH = 733 Hz, νP-H = 2430 cm-1) (1) and other equatorial hydridophosphoranes (3). These observations are reconciled with an apical P-H disposition for 1a in solution on the basis of a correlation between 1JPH and ligand electronegativity (Equation 1). This was developed using data for a large number of hydridophosphoranes 1JPH = 306 [σI(equatorial) + 0.505σI(apical)] + 595
(1)
which could, with some assurance, be assigned TBP structures with equatorial P-H bonds. Apical hydridophosphoranes 1a, 1b, and 3 (3, 4) a l l have 1JP-H values much lower than Equation 1 predicts. The apical P-H bond length of 1.35(3) Åfor 1a is, within experimental error, the same as that reported for the equatorial P-H bond of 2, 1.32(3) Å, and for the apical P-H bond of 3, 1.349(71) Å (2). A l l are shorter than the sum of phosphorus and hydrogen covalent radii, 1.40 Å (4), and considerably shorter than P-H bond lengths in a variety of hydridophosphines and in the PH + cation, 1.41-1.45 Â (5). The two apical P-0 bonds for £ (average value = 1.745 Â are in the usual range of bond lengths for such species (6). The P-0 bond for TJj (1.825(3) Â is longer. 4
7
Current Address: Monomer Process Research Department, Rohm and Haas Company, Research Laboratories, Spring House, PA 19477 0097-6156/81/0171-0429$05.00/0 © 1981 American Chemical Society
PHOSPHORUS CHEMISTRY
430
Table I .
Bond L e n g t h s (Â) and A n g l e s (Deg) i n H y d r i d o p h o s p h o r a n e s
Bond L e n g t h , Angle
a b c Làb& Zed Z.ac Ζ ad Z de Z.ae Ice
Compound la
a
1.825(3) 1.35(3) 1.825(3) 176(1) 112.7(1) 90.7(1)
— 123.6(2) 85.5(1) 123.7(2)
2
a
3
1.743(2) 1.748(3) 1.32(1) 178.47(3) 114.5(11) 86.1(11) 88.09(14) 127.6(2) 88.48(14) 117.9(11)
b
1.986(5) 1.35(7) 1.577(3) 172.2(48) 120.0(1) 87.6(1) 87.1(2) 119.3(3) 87.6(1) 120.0(1)
9
C
1.721(2) 1.701(3) 1.36(3) 177.4(1) 115(1) 91(1) 90.8(1) 123.7(1) 92.6(1) 121(1)
Reported h e r e i n . R e f e r e n c e (_3). R e f e r e n c e ( 1 0 ) . The 0-P-H angle f o r ^ i s bent toward the t-Bu a r y l group; the N-P-H angle f o r ^ i s bent toward one e q u a t o r i a l oxygen; ^ and ^ have 0-P-P angles bent away from the e q u a t o r i a l hydrogen. The p h o s p h o r u s atom l i e s 0.036 Â b e l o w t h e e q u a t o r i a l p l a n e o f toward the a p i c a l hydrogen. T h i s r e p r e s e n t s a s m a l l d i s p l a c e m e n t a l o n g t h e pathway f r o m t h e i d e a l TBP t o w a r d ^, w i t h P-0 bond l e n g t h e n i n g and P-H bond s h o r t e n i n g . Addition of trifluoromethanesulfonic ( t r i f l i e ) acid to a CDCI3 s o l u t i o n o f ^ Q^) gives alkoxyhydridophosphonium s a l t ^ (^). H e l l w i n k e l ' s (7) b i c y c l i c p h o s p h o r a n e £ b e h a v e s i n an a n a l o g o u s manner. An i n c r e a s e o f a b o u t 300 Hz i n t h e v a l u e o f "SlPH upon f o r m a t i o n o f ^ , J j f r o m i s consistent with a smaller d e g r e e o f p h o s p h o r u s s - o r b i t a l c h a r a c t e r i n t h e a p i c a l P-H bond o f t h e p h o s p h o r a n e (p/2 h y b r i d i z a t i o n ) t h a n i n t h e s p ^ p h o s p h o n i u m P-H bond ( 8 ) . The c o n v e r s i o n o f ^ t o ^ c a u s e s o n l y t h e s m a l l change (17 Hz) i n "**Jp_ e x p e c t e d f o r a s m a l l e r change i n s - o r b i t a l character (ca. sp^ to s p ^ ) . I n o u r p r e l i m i n a r y c o m m u n i c a t i o n (jl) we r e p o r t e d a pKa o f 11.7±0.1 f o r l b . U t i l i z i n g t h e same P NMR t e c h n i q u e we f i n d pKa = 10.3±0.2 f o r W h i l e the s t r u c t u r e of the conjugate base o f 2, p h o s p h o r a n i d e ^ can be u n a m b i g u o u s l y a s s i g n e d ( s e e c h e m i c a l s h i f t models and ^ ) ( 1 1 ) t h e same s t r u c t u r a l a s s e s s m e n t i s not as s a t i s f y i n g f o r the conjugate base of ^ (or ^ ) . Phosphine d e r i v a t i v e s (12) have 31p NMR c h e m i c a l s h i f t s s i m i l a r to those seen f o r the conjugate bases of ^ (-9.92 ppm) and ^ (-11.1 ppm). Weak P-0 b o n d i n g w o u l d n o t , h o w e v e r , be e x p e c t e d (13) t o l e a d t o a s i g n i f i c a n t u p f i e l d ^ l p s h i f t i f t h e bond i s a s u f f i c i e n t l y weak one. E s t i m a t e s o f pKa v a l u e s f o r t h e e q u i l i b r i u m b e t w e e n o p e n - c h a i n t a u t o m e r o f ^ and i t s c o n j u g a t e o p e n - c h a i n base c a n be u s e d w i t h t h e measured pKa v a l u e f o r ^ and t h e H
3 1
88.
Ross
AND MARTIN
Monocyclic
C F
F
Ο
3^
C F
^ 3^ 3 O"
Ph-
3 OH
CF S0 -
Η ί α , X =^-Bu, δ »b, X = Η, δ
3 1
3 1
p + 10.2 ^Jpjj = 569 Hz)
P + 11.7 ^Jpjj = 560 Hz)
CFo CFo 3 -OH
F
^ 3^
C F
3
6H ^CF SO ' 2
CF3SO3Η
3
C F
f
CF C F 3
δ
3 1
3
-Ph
P h - ^ |I
jj"**Ph
Ρ
C F
3
Η
431
Triarylalkoxyhydridophosphorane
Ρ + 2.75 ^Jpjj = 730 Hz)
δ
3 1
3
S
3 °3
3
1
P + 38.5 ( J
p H
= 716 Hz)
PHOSPHORUS CHEMISTRY
CH N-T|b
C
3
Ρ
-25.9 CF3CF3
X
OCÎ
Ό Ρ: " L i
+
Ph-
13 X
, δ
3 1
P + 113
X δ
, X = CFg, Y
3 1
Ρ
H,
=:
-18.5 , X = CFg, Y — CHg, -17.9 -35.0 or
, X = CHg, Y = H,
OC -Χ
Ph-
P:
I
Ph δ X = -C(CH ) OCH Ph, 3
2
2
3 1
Ρ
X = -C(CH ) OH, 2
-11.1
X = -CH OH,
-16.0
3
2
X = -C0 H, X = -OCH ,
«·
P:
Ph^^l Ph
-5.0
2
b
-13.5
3
X = -HC(CH K>H, X = -CF , 3
0
O"
+21.9
-17.0 -10.9
21 (δ 31P O
A
-
9.92
ppm)
88.
ROSS A N D
MARTIN
Monocyclic
Triarylalkoxyhydridophosphorane
433
e x p e r i m e n t a l lower l i m i t f o r t h e f r e e energy d i f f e r e n c e between ^ and i t s u n o b s e r v e d o p e n - c h a i n i s o m e r t o d e t e r m i n e t h a t t h e l o w e r l i m i t t o t h e energy d i f f e r e n c e between t h e t r u e c o n j u g a t e base o f (either o r ^Uj) a n d t a u t o m e r fyfo i s z e r o . There i s t h e r e o r e no d i r e c t e v i d e n c e r e q u i r i n g t h a t we p o s t u l a t e e n e r g e t i c a l l y s i g n i f i c a n t P-0 b o n d i n g i n On t h e o t h e r h a n d , s i n c e we have o n l y a lower l i m i t f o r t h e energy d i f f e r e n c e between ^ and i t s o p e n - c h a i n i s o m e r , we c a n n o t r u l e o u t some P-0 b o n d i n g i n ^J.. F u r t h e r w o r k w i l l b e r e q u i r e d t o remove t h i s a m b i g u i t y . T h i s r e s e a r c h was s u p p o r t e d i n p a r t b y a g r a n t the N a t i o n a l Cancer I n s t i t u t e .
(CA13963) f r o m
Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
13.
Ross, M. R.; Martin, J . C. J . Am. Chem. Soc. 1981, 103, 1234. Milbrath, D. S.; Verkade, J . G. J . Am. Chem. Soc. 1977, 99, 6607. Clardy, J . C.; Milbrath, D. S.; Springer, J . P.; Verkade, J . G. J . Am. Chem. Soc. 1976, 98, 623. Brazier, J . F.; Houalla, D.; Loenig, M.; Wolf, R. Top. Phos phorus Chem. 1976, 8, 99. Pauling, L. "The Nature of the Chemical Bond"; Cornell Uni versity Press: Ithaca, N.Y., 1973; p 224-228. Corbridge, D. E. C. Top. Phosphorus Chem. 1966, 3, 91. Holmes, R. R.; Deiters, J . A. J . Am. Chem. Soc. 1977, 99, 3318. Hellwinkel, D.; Krapp, W. Chem. Ber. 1978, 111, 13. Hoffmann, R.; Howell, J . M.; Muetterties, E. L. J . Am. Chem. Soc. 1972, 94, 3047. Musher, J . I. Angew. Chem., Int. Ed. Engl. 1969, 8, 54. Clark, T. E . ; Day, R. O.; Holmes, R. R. Inorg. Chem. 1979, 18, 1653. Granoth, I.; Martin, J . C. J . Am. Chem. Soc. 1979, 101, 4623. Granoth, I.; Martin, J . C. J . Am. Chem. Soc. 1981, 103, in press (compound 14); Landvatter, E . ; Rauchfuss, T. B.; Wrobluski, D. A., private communication (compounds 16, 19); Granoth, I.; Alkabets, R.; Shirin, E . ; private communication (compound 15); Wrobluski, D. A.; Rauchfuss, T. B. Inorg. Synth., submitted (compound 17); McEwen, W. E . ; Shiau, W.-I.; Yeh, Y . - I . ; Schulz, D. N.; Pagilagan, R. Α.; Levy, J . B.; Symmes, C. J r . ; Nelson, G. O.; Granoth, I. J . Am. Chem. Soc. 1975, 97, 1787 (compound 18); Miller, G. R.; Yankowsky, A. W.; Grim, O. S. J . Chem. Phys. 1969, 51, 3185 (compound 20). Granoth, I.; Martin, J . C. J . Am. Chem. Soc., in press.
RECEIVED
July 1, 1981.
