Before I answer your question, I want to add the contextual note that in this period of time, "Chinese communists" has to be used somewhat loosely and can only somewhat relate to the Communist Party of China which formed in 1921 as a result of a whole host of events including revolutionary thinkers recruited from Europe, the May 4th movement, WWI, etc. etc. This is over a decade after the Xinhai Revolution which toppled the imperial system in 1911-12. Communists had existed in China before 1921 but even by the mid-20s, the party's membership was very small. I'm also slightly confused about the exact period of your question. There was a great deal of turmoil that followed the end of the Qing and Sun was actually exiled for a period of time afterwards due to a number of political events that saw former Qing official and general Yuan Shikai assume the presidency over the newly declared Republic of China followed by a period of warlordism. Sun saw the communists as a bigger piece of the puzzle when it came to his quest for eventual revolutionary reunification of the entire country and I'm not too sure they played that big of a role in 1911.

Anyways, I have been able to find relatively little regarding Sun Yat-Sen's exact sympathies towards the CPC and Chinese communists. However, his wife Song Qinling is known to have written a letter addressing the treatment of the political Left within China. This, along with the historical record, can help us piece together a picture of how Sun regarded the communists. Dr. Sun most definitely recognized the importance of working with the Communists during the revolutionary and early state-building era of post-imperial China. He is known to have had diplomatic contact with the Soviet Union going at least as far back as the Bolshevik victory over White forces in 1918. The Soviets were keen on establishing a Communist presence in China and were a major player in the creation of the CPC in 1923. The Soviets also helped to broker an alliance between the GMD and CPC in late 1923, shortly after the formation of the CPC proper. Sun worked with the Soviet agent Mikhail Borodin to eventually allow for the 'merger' of CPC members with the GMD despite facing backlash both domestically and from overseas. Nonetheless, Sun persevered on the path, apparently proclaiming that if the CPC was not to be allowed to cooperate with the GMD in its nation-building project, then Sun himself would "join the CPC".^(1) With a lack of primary sources, it is difficult to determine what Sun meant by this statement. I hesitate to declare it as evidence of a high degree of sympathy due to the politically expedient nature of events surrounding the matter. Sun understood the danger of factionalism and to alienate the CPC, however small it was back then, was to Sun a wasted opportunity to either increase the KMT's own position or at least help stabilize China somewhat. Sun's wife Song writing in the fall of 1927 seems to mirror this mood somewhat. Keep in mind that by now, Sun had died of liver cancer and Chiang Kai-shek had taken over leadership of the KMT, greatly increasing factionalist tension. Song writes:

"... peasants and their leaders, workers and their leaders, Communists and their leaders, who labored in order that the Guomindang power might reach the Yangtze, have been ruthlessly and wantonly killed... because so-called 'leaders' of the Guomindang - petty politicians reverting to type - believe that they can violate Sun's [legacy] and rely on the new militarism to carry out the stupendous task of the revolution..."^(2)

Sun through his interactions with the Soviets and Chinese communists seemed to be a keen political player. He at the very least recognized the political value of the communists, irrespective of how much or little he agreed with their exact politics and methods. Sun's wife seems to echo a certain degree of sympathy in her letter. It seems that the Communists themselves might have had more of an issue allying and partly merging with the KMT than Sun did with the CPC, but that is a different story. What he planned on doing with the CPC after he achieved his goals of Chinese reunification is a different matter altogether and something I would consider speculative and therefore bad history.

^(1) The Search for Modern China. Jonathan Spence. 1990. 338.

^(2) "Madam Sun Yat-Sen Defends the Left" in The Search for Modern China: A Documentary Collection, Third Edition. Jonathan Spence, Janet Chen, Pei-Kai Cheng, Michael Lestz. 255-257

Edited for minor date error