COX~IUNICATIONS TO THE EDITOR
May 5 , 19ti2
li67
DIMETHYLAMIDODIFLUOROPHOSPHINE TETRACHB)IBIHS-A STABLE ADDUCT OF
Experimental.-A 1.8-millimole sample of B4HsCO was condensed into a reaction tube on the B& vacuum line; a 1.8-millimole sample of F2PN(CH3)2 Sir : was frozen on top of the BdHsCO using liquid Nz. In 1939 Burg and Spielman' found that CO The tube was warmed slowly to -20' whereupon under pressure removes a BH3 group from BsHll a gas came off over a 10-min. period. The system to give the unstable compound B4H8C0. T h e then was warmed to room temperature, and ' ) liberates up to 6070 of its stirred in the vacuum line for 30 minutes with a liquid (v.p. 71 mm. a t 0 CO on standing for 12 hours at room temperature. magnetically operated "hopper type." stirrer. The analogy between PF3 and C 0 2 suggested t h a t After the system was frozen with liquid N2, the PF:j might displace CO to give a more stable Ffj- non-condensable gas was separated and recognized PBIHS. A displacement reaction did indeed occur, as CO (1.8 millimoles) b y its molecular weight of 28 but the compound formed, presumably F3PB4H8, (vapor density). The condensable product was was unstable under the conditions of the experi- distilled from a trap a t 0' into traps a t -22' and ment and never could be purified in our vacuum - 196'. The clear liquid product was found in the system. T h e low basic strength of FaP would -22' trap; only a trace of material was found in the appear to be a probable cause of compound in- - 196' unit. Alnalysisof the purified liquid prodstability. -Ittempts to stabilize the B4Hs complex uct (m.p. -18') showed: H , 8.52; N , 8 . 5 i ; C, by replacing CO with t h e stronger base N(CHaj3 15.15; hydridic hydrogen, 4.61. Theoretical for were likewise unsuccessful.' In this research i t was F2PN(CH:I)2B4H8is: H,8.38; IYj 8.32; C, 14.Gl; found t h a t X(CH3j3is such a strong base t h a t it hydridic hydrogen, 4.91. .Uhough boron, fluorine, attacks the B4H8 group to give (CH;J3XBH3and and phosphorus were not determined directly, the other products. above results coupled with the stoichiometry of Recently it has been found t h a t the newly syn- synthesis leave no reasonable alternative to the thesized ligand3 F2PN(CH3)* will form a stable empirical formula (CHa)&PF2B4Hs. The molecular weight of the sample, measured by freezing adduct with B4Hs. T h e reaction is BdH8C0 F ~ P N ( C H ~-2oe ) ~ ( C H ~ ) ~ N P F ~ B ~co. H ~ In a point depression in benzene, was 1-59f S as comformal sense F2PN(CH3)2can be considered as a pared to a value of 165.4expected for the above composite of F:?Pand N(CH:& and seems to com- formula. The vapor pressure of the liquid over the bine the required features of both. T h e clear temperature range 22 to 33.5 is represented b y the liquid compound FrPN(CHa)yB4Hs can be heated equation l o g P = - 1 7 2 7 / T + 6.128 to 35' without significant decomposition, but above VAPORPRESSURE OF ( CH3)2SPF2B1Hs 53' a sudden break in the vapor pressure curve indicates decomposition. The compound melts at T , O K . 295.5 300.9 306.2 318.7 326.6 -1s' and has been stored in a dry box a t room Obs. v.p. (mm. Hg) 1 . 9 2 . 5 2 . 9 1 . 9 7.4" temperature for more than a week. X slight yellow Calcd. v.p. 1.9 2 . 5 2.9 5.1 6.9" color developed on storage, but the infrared specDecomposition rapid above 326.6. trum of the stored sample was identical with that of The heat of vaporization over the temperature a fresh sample. ,I\lthough the ligand (CH3)?NPF2has two possi- range studied is estimated as 8,000 cal. although ble coordination sites, the preliminary spectro- the precision of the value is low in this region of scopic and chemical evidence leads us to believe very low vapor pressure. The molecular weight of that the B4HB group, with geometry comparable to the vapor, as estimated b y gaseous effusion, was the boron framework of B4HL0, is coordinated only 160. Acknowledgment.-The generous support of this t o the phosphorus. Structural and chemical work by the Sational Science Foundation is studies are in progress. gratefully acknowledged.
BORANE-8-F2PN(
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(1) A . B. Burg and
5. R.
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Spielman, J. A m . Cheirt. SOC.,81, 3179
(1939). (2) R. 1V. Parry and T. C . Bissot, ibid , 78, 1524 (1936); R. W. Parry and I,. J. Edwards, ibid.,81, 3.544 (19jY). ( 3 ) Sr. 31. A . Fleming and R . W.Parry, to he IJublished.
DEPARTMEST OF CHEMISTRY GARYTERHAAR 'CNIVERSITY O F MICHIGAT S R . h I A R Y ;\LBERT FLEMISG .INS*ARBOR, MICHIGAN ROBERT JV. PARRS RECEIVED MARCH 3 , 1962
